That's a pretty broad, non-specific question. First, it really depends on having good production dialog. If the recording was shoddy, there's not much of anything you can do in post to make it right.
Second, assuming that's not the issue, it's hard to know where the problems are without hearing what you're hearing. A posted sample would be helpful. I could give you a rundown of things to do, but there's no magic number for any one setting on any one plug-in as it all has to be set depending on the source of each clip.
Last, the mixing environment is very important. Is your room treated at all? I mean, even a cursory application of acoustic foam can be helpful in knocking down reflections. Plus, a decent set of monitor speakers, properly calibrated to mix level, is a must. Cheap speakers, and monitors that are too quiet, are misleading. And if you're mixing on headphones, don't expect any acceptable results.