Like any successful voice-over artist will tell you, becoming a pro in this industry takes more than the voice-over training. There's a website to build, marketing to plan, Pro Tools to master, and then there are little "details," like what information to include in a contract. Make sure you have your ducks in a row when you land your first voice-over job so that you look like the pro in the client's eyes that you sound like!
Sending the client a contract is a good idea so that both you and the client are explicit about the details of the project, the timeline, the agreed upon price, and the deliverables -- including how many iterations of the voice-over they get for the rate. In most cases, a standard template in Microsoft Publisher will suffice. Devise a contract template ahead of time, complete with your brand name and logo, which will save you time later on.
You may run into a situation in which you will go back and forth with a client through email about the details of the voice-over job, but it's generally a good idea to summarize everything in a contract one last time. The organization will be appreciated by the client, and documenting your projects will make it easier for you in tax season!