Hey Guys:
I'm wondering if we could use this as an on-going thread for mixing tips.  Maybe newbies could come here to get a quick start, and even those who have been mixing a while can learn something. 
I'll offer two for starters:
 
1.  When EQing think in terms of subtracting rather than adding.  If a guitar is conflicting with the vocal rather than boosting the vocal, subtract from the guitar.  You might start with a high-pass filter and start carving off the bottom of the guitar until the vocal starts to pop out. 
 
2.  Mix in mono.  It forces you to shape the sound of each instrument in relation to all the others.  Then when your mix sounds great in mono, pan it out.  It will sound glorious!!
 
Others?