A lot of pop music, especially dance tracks, are compressed/limited to death at the mastering stage so that they sound at least as loud or louder than other similar productions. Since peak transients can't ever be louder than digital zero, what is happening is that all the material below that is being squished into a narrower dynamic range and brought up closer to the peaks. Done to an extreme degree you can make an incredibly loud, but often unmusical, recording. If you are going to have your material professionally mastered, it is generally recommended that you don't try to accomplish this yourself (with a finalizer, etc) - or else you risk taking all the flexibility to improve your tracks away from the mastering engineer.

I would say just make your mixes sound good. Use the available dynamic range (no sense having your peaks at -6) Leave worrying about final volume to the mastering stage. There is no easy formula to setting levels of drums, bass, guitars, vox, etc. relative to eachother - because your ears will want to hear different ratios depending on song style, arrangement, and orchestration. So that's what it always comes down to - ears.