Oliver Peters has an article about how he handles audio in his video projects. I don't necessarily think his process is best for every project, but there are times when this approach is needed. At the very least, you should be applying compression to your final export on every project, but on more complicated projects, you often need to approach the mix as you would in a recording studio.
This article talks about mixing in Soundtrack Pro, which is a good option. For even more control over the quality of your sound, consider a program such as Steinberg Nuendo. I have used Nuendo for more than ten years and cannot recommend it highly enough. In my next post, I will offer a comparison between it and ProTools. Whatever the case, the point is to give attention to the audio mix--realizing that you can only do very limited sweetening on the timeline in Final Cut, Media Composer or Premiere Pro. Read the article here.