Listen to voiceover reels on the Internet to get an idea of what one sounds like. There are generally two types of voiceover categories: the Announcer Voiceover and the Regular Voiceover. The Announcer Voiceover is more commanding and direct, with a strong, sales-type authority.
Find a script that you can record as your own. There are sites on the Internet that specialize in making voiceover scripts available. It is has also been common practice to record commonly known television commercials in your own voice.
Practice your scripts. Make sure you know the lines perfectly. The clearer and more confident you sound, the better the recording will be.
Record several different samples of the scripts. Use a variety of different vocal ranges if you are capable. You can also include accents if you are capable of speaking them well.
Mix your sample voiceovers together onto a CD, as well as a digital file. The voiceover reel should be no more than 2 minutes long. A professional recording is always recommended if you can afford it. The cost can run from a few hundred dollars to several hundred. You can also do this at home using digital audio recording software on your computer.