Be ready before you interview agents. Have your marketing materials ready to impress them. Good examples of this would be from any compiling mailing lists, promotional material, demos, and a website.
Self-direct your voice over auditions only when you are ready to. If you are not ready yet, seek guidance and input from peers. For the next step, join an actors’ union in order to protect yourself, upgrade the quality of projects over time.
As the quality increases you should be able to up income. The whole idea is to never stop pushing your abilities past the success you establish.