There are lots of ways to get voice acting work, from online sites such as Bodalgo.com, Mandy.com, Voice123 and Voices.com. These are known as pay to play sites. They have lots of opportunities for you to audition, but it is highly competitive. Looking locally for businesses, including radio stations, that need voiceover is also a good way to start.
Both union and non-union have advantages and disadvantages; ultimately, it’s a decision that you, as a voice over actor, will have to make. Like everything else, it’s of critical importance that you do your research and weigh up the pros and cons. Seasoned pros will usually tell you it’s best to be a union member because, if you run into trouble, the union will fight your cause.
You start off each job as a producer, consulting your client and getting briefed on the project at hand. Then you become an engineer, dealing with recording gear and software, setting the mic position and levels. Next, you step up to the mic as an actor, bringing the script off the page and connecting with the listener. Meanwhile, the director in you sits behind the metaphorical glass, making sure the actor doesn't mispronounce a word or stumble through a passage of text. Then you're an editor, cleaning up the best take and sending the resulting audio to your client. You need to be able to perform all of these roles to a high standard, and the better you are at each, the more your business will prosper.