Caveat:  The voiceover demotape will ultimately get you a VO job or keep you from being hired.  The casting director, agency representative, or whoever is making the voice selection decision, listens to numerous tapes and decides which voice talent will get the job.  If your tape is selected, that's great as long as whatever is on your demotape is able to be reproduced on short notice, with minimal practice, and without direction at the studio.  If there is even the slightest question in your mind that you can do all of that, keep practicing before sending out your tape.
      Lots of people cobble a demotape together and send it out.  Being able to actually do the job under difficult conditions is what gets you a second job.  They did great working with their voice coach.  They did great when they could practice a 30-second script for several days.  They did great when they had terrific direction from someone who knew what they wanted and knew how to convey their desires to the talent.  Quite often, when they get a job they quickly realize that they cannot duplicate their on-tape performance in the studio.  Unfortunately, so does everyone else and the chance of a second job is very slight.

Terms:  Some definitions may help to better understand what follows:

• Copy: The script being read is referred to as "copy."
• EFX: Effects, could mean voice effects or sound effects.
• Engineer: The person in charge of recording and mixing audio.
• Mic: Short for microphone.
• Producer: The person in charge of creating the commercial.
• Production: The mixing of voice, music and effects together into a final product.
• Read: You are expected to be able to read the words on a page of copy, but you are also expected to be able to give a good "read," meaning you are performing the spot well.
• Script: The words that will be read in the commercial.
• SFX: Sound effects, like thunder, not voice effects.
• Spot: A commercial.
• VFX: Voice effects, not a standard term, refers to adding echo or other effect to a recorded voice.
• VO: Short for voiceover.
• Voiceover: A recorded voice where the speaker is not seen by the listener, viewer.

The Demotape:  A voiceover demotape is not necessarily a physical tape anymore.  These days, the demo "tape" can be a compact disc (CD), a computer file in any of several formats, a link on the Internet, or the ubiquitous cassette.  As the demotape is further discussed, keep that in mind.  A "demotape" is no longer necessarily physically on a tape.
      The voiceover demo is the voice artist's resume.  The person listening to the demo decides if the voice on the tape will fit the product.  In general, the people who get the majority of work can demonstrate a range of capabilities.  They are able to read at various speeds, with different vocal and tonal qualities and can sound like different people.
      If the demotape is on CD, there are probably several tracks for an accomplished voice artist.  One track for the standard commercial demo.  One for narration.  One for character, or cartoon, voices and, finally, one for imaging/positioning, or radio/TV announcing.  It isn't necessary to have all of these tracks on your demo.  You only need to have one track that shows what you can do.
      The normal demotape/track is anywhere from one-minute to two-and-one-half-minutes in length.  Anything longer than that is probably a waste because the casting person generally won't listen all the way through.  Most will figure that if they haven't heard what they are looking for in two-minutes, they probably aren't going to.

Your Demo:  In general you need to have a minimum of four to six different spots on your demo.  If a spot calls for sound effects or music, it should have the appropriate sounds and music mixed in at appropriate audio levels.
      The spots should show your range.  One spot where you sound concerned.  One spot where you are happy.  One spot in which you speak excitedly, and one spot where you sound sexy.
      The best spot, your bread-and-butter voice, should always go first.  The next spot should be significantly different in style from the first.  By changing styles in this way, it amplifies the range capability of the artist.  Changes in style should continue throughout the demo so the casting person doesn't feel that the person sounds "the same" in all the spots.
      When speaking about "the best spot," it means just that.  Simply because the voiceover is the best doesn't mean the spot goes first if the rest of the production is below par.  Alternatively, a commercial with outstanding production levels should not go first if the voiceover is poor.  There is a balance between the voiceover quality and the rest of the production.  The best voiceover with the best production goes first.  The next spot is the one with the next-best voiceover and the next-best production levels that ALSO shows a significant change in the artist's style.

Scripts:  Commercial scripts are available all around you.  They are on the radio and TV, just waiting to be recorded and transcribed.  They are in the newspaper and magazines, although you may have to rewrite them a bit.  The back of a cereal box is a script if you want it to be.
      Try to find scripts that can demonstrate your range.  If all your scripts are the same type, you'll always sound the same.  In that case, you'll only be considered for a very narrow range of commercials.  You may say that you are uncomfortable doing some kinds of commercial.  Work especially hard on that type of commercial until you aren't uncomfortable anymore.  If you get hired to do a spot, you don't have control over the type of spot you are going to do.  You arrive at the studio.  You are handed a script.  At that point it's too late to turn around and tell the Producer that you don't do this type of spot.  Actually, it's not too late, you can do it, but you'll never work for that company, that agency, in that studio or for any of the friends of any of those people.

Spots:  Because you recorded a 30-second spot doesn't mean you have to put the entire 30-seconds on your demo.  In fact, I'll give you a big hint: Don't put the whole 30-seconds on your demo.  Obviously, that goes double for a 60-second spot!  Casting people only need to hear enough of a spot to determine whether you were able to "pull off" the character you were portraying in the commercial.  Keeping the cuts short, keeps the casting person interested and listening.
      The length of each cut used in the demo depends on how much was needed to show you could do the job.  That could be 5-seconds, or it could be 20-seconds.  As you assemble your demotape, you can always remove some later.  Put your spots in order, then start cutting.  You're not trying to put a tape that you like together.  You're putting together a tape that will get you hired.  Edit the demo for the casting person, not yourself.
      A good voice artist should be able to handle two-person copy.  These are scripts that include a second voice artist, not scripts where you read more than one part.  If you are going to include a two-person spot in your demo, you should only use spots where the other person is of the opposite sex.  You don't want to get a call from a casting person asking you to connect them with the other voice on your demotape.  It may be your best friend, but let them send out their own demo if they want the job.

Production:  The professional demotape is not created by recording into the little pencil-like microphone on your computer.  You need an isolation booth or very quiet, sound-deadend room and a good quality microphone.  The microphone is the biggest problem for most people.  A decent microphone costs about $100 US.  Yes, you can get less expensive microphones, and yes, you can get microphones that are more expensive and still make poor quality recordings.  The trick is to have a good quality microphone that will work in the proper environment with the available equipment.  Most high quality microphones won't work with your standard computer sound card.  Most computer sound cards in the normal home PC are not made to record high quality audio.  That doesn't mean your standard home computer and pencil-style mic can't be used for practice.  If you sound good on a poor microphone, you'll sound great on a good quality system.

      Music/SFX: Once you have your voice recorded, you need to complete the production of the spots.  You may need to add music and/or SFX.  You may need to add effects to the voice itself, such as an echo effect.  Be aware, lots of people become enamored of their voice effects.  If all of your spots have an echo added to the voice, the casting person is going to find it difficult to know how you will sound without an echo.  Voice effects must be used sparingly.
      Sound effects and music can dramatically enhance a commercial.  This is not to say that you must have one or both in every spot you create or use on your demo.  A well read, voice-only spot can be very powerful.  At the same time, if you do use SFX or music, the audio levels must be such that the voice can still be clearly heard.  Background music is just that and needs to remain in the background.  Be very careful of heavy bass beats in your musical selections, for example.  Even when the music level is low, the bass beats can drown out the voice.  Sound effects have the same difficulties.  The levels must allow the voice to be heard.  If a loud effect is needed, it should occur when the voice is silent so as not to cover it.
      Music and SFX must be applicable to the spot.  When creating a soft, sexy perfume spot, ragtime jazz is probably not appropriate for background music.  When your spot appears to take place in the passenger section aboard a commercial jet liner, the sound of a single-engine propeller airplane is not the best choice of sound effect.  Additionally, you have the legal obligation to own the rights to the music and SFX you use in your spots.  Using copyrighted material without permission is illegal, although most of the time little will be said.  None the less, it is something to be considered.

      Home Recording: Even though there are low-cost audio editing and multi-track mixing programs available, most people will have difficulty creating a professional quality spot for use on a demotape.  If you want to try recording and editing your own material, I recommend GoldWave and MultiQuence.  The demonstration versions of the software are full-functioning, with minor restrictions, and the programs are inexpensive if you wish to bring them to their full potential.  There are more expensive and more capable programs, but for the majority of people, especially those new to recording, editing and mixing, these software packages are more than adequate.
      When you add up the cost of the microphone and software, and assuming you already own a computer, you are looking at a minimum of $200 to $250 US.  Add in the relative cost of the time it will take to learn to use it all, the learning curve, and it will be almost as much as producing your tape in a studio.  This is especially true if your skills are such that your demotape turns out to be less that professional.

      Studio Recording: The alternative is to go to a studio to record your material and get an engineer to edit your spots together.  This can be expensive.  Very expensive.  A decent studio will charge a minimum of $75 to $100 US per hour, but many will charge considerably more.  A qualified editor/engineer will charge about the same amount for their time.  There may be an additional charge for the equipment use, especially if it's in the studio.  Unfortunately, they may not have a lot of experience creating voiceover demotapes.  The reality is that not a lot of people do have that experience.  You may actually have to make a great deal of the decisions on how your tape is put together.  No matter how you slice it, you're looking at a minimum of $300 to $500 US to studio produce a basic VO demotape.  Most people will spend upwards of $1,000 US to produce their demotape.

Packaging:  Once your demotape is complete, be it a cassette or CD, you need to make copies to distribute.  If you have your demo on cassette, never, Never, NEVER make a copy from a copy.  Always make your distribution copies from the master tape.  If your demo is on CD, you can make copies on your computer if you have a CD burner.  Regardless of the format of your demotape, always play it on your personal stereo system to make sure it plays correctly.  Don't play the CD on the computer on which it was created, play it in a standard CD player.
      Cassette cases have what's known as a "J-Card," the cardboard sheet inside the case that tells what's on the cassette.  CD cases can have a cover sheet, a back sheet and an edge sheet/spine, which is usually part of the back sheet.  You will also need to make labels to be directly placed on the CD or cassette.  If you have a computer and a decent printer, you can probably make these yourself.  You can also go someplace like Kinkos to have them printed for you.
      Your demotape is your voiceover resume.  You wouldn't apply for a job with a handwritten resume or one with misspellings or smudges.  Create a nice cover for your demotape.  Packaging counts.  Include your name and phone number on the case as well as on the cassette or CD.  If the CD gets separated from its case, you want your name and phone number on the CD so they can contact you.
      Unless you are also attempting to be on-camera for TV commercials, I don't recommend putting your picture on your demo labels or covers.  People sometimes assume you sound a certain way based on your looks.  If you want to send a photo, send a nice head-shot separate from your demotape.  You can include your address.  If you are sending a CD with several tracks, you should include a table of contents, usually inside the front cover, telling what each track contains.
      You may want to add a disclaimer to your packaging.  Do this if you don't have commercials you were paid to voice or if you created your spots specifically for your demo.  Just include a notice in small letters that says, "These recordings were created for demonstration purposes only."  This can cover you if you use a script used in a commercial produced by the person listening to your demo.  They hear "their" spot and know you weren't the talent used.  They might think you're trying to get hired by representing yourself as having voiced a spot you didn't.  The disclaimer should to be large enough to be seen and read, but not too large.