In episode 50 of The Audacity to Podcast, Daniel J. Lewis offers recommendations to improve your voice quality even from a cheap, consumer-grade microphone. In fact, you don't even need to listen to the podcast, as the show notes are pretty good by themselves. However, listening will actually allow you to hear the differences as they're being applied.
In episode 81 of the same podcast, Daniel also covers 5 tips that helps audio quality with any microphone.
Check these out, and play with the recommendations to find your best workflow. Even if the project producer requests that no post-processing be performed, the mic and mouth placement recommendations can help them get the best sound for their projects.