Mixing has definitely been one of my weaker skill-sets when it comes to music production, so over the years I’ve read tons of books, guides and magazine articles and watched loads of videos on the subject of mixing.
Personally I try to spend more time now, in the beginning stages of my production, just making sure that the sounds that I’m using are very good quality and sound good on their own. I find this makes mixing down the song afterwards a lot easier, as I don’t have to worry about making each audio track/channel sound better or listenable, but rather on the overall balance of the sounds.
In the end, despite all of the advice and tips that you can gain from those sources, it does just come down to, as Sonicbyte pointed out, giving your song’s core elements space and prominence in the track, so that your listeners know what you want them to hear.
Having said that, if you would like help with mixing in a specific genre, or learning different mixdown techniques, then feel free to ask here in the forums, or track down some of the thousands of articles and videos available on the subject.
A word of warning when it comes to finding advice on this subject (and on anything regarding music composition/production/engineering), though: Be wary of anyone saying that there is one ‘best’/’only’ way of doing things. There’s no one plugin or technique that will make all your songs perfect, of course, and it purely comes down to what works for you and your music.