The best tip for how to start in voice acting includes practicing voices and acting. Try to get involved in local theater, take a few drama classes and practice doing different voices until you can transition easily from one to the other. Think of the voice overs that Robin Williams did in MRS. DOUBTFIRE and how many hours of practice in acting he had to complete to hit those smooth transitions.
Cut a demo of you acting in various voices or even reading a short section on how to start in voice acting, or auditions and how they work. Try to come up with a collection of several short monologues in different emotions. For example, you may want to have one angry character, one happy character, one sad character and so on. Use a professional studio for your demo. These can be found in most major cities, but Nashville, Los Angeles and New York are probably the most prolific in cutting demos.
Make copies of your demo CD and send to agents. It is nearly impossible to break into voice acting unless you have an agent these days. Your first goal should be to land that agent. Actors unions list agents (AFTRA and SAG). See more in the resources section.
Audition for the parts you want. Once you have an agent, you will likely be asked to go on auditions. Try to make your audition stand out from the crowd by putting some of yourself into the audition. Physically act out the part, even though no one will see you if you land the voice role.