Speaking of compression, Matthew Weiss:
Rap is generally an in-your-face, visceral style of music. The kick is physical, the snare is physical, subtlety isn’t really the overall goal. And the vocals are paramount. I’ve mixed a number of rap records where the vocals are lower in the mix, but never have I thought it was a good idea. Generally I want the vocals to be equally as strong as the drums or stronger, and I want them as “forward” as possible. Compression is usually a part of that equation.
There are some really good ideas in that post. And it applies beyond rap music – it’s a useful way of approaching any vocals that need to be thick and aggressive. It’d be just as useful for rock or metal.