When I am mixing my own material I tend to just record at around -12db and then after using my guitar, compression, EQ etc. I am at around the -9db level. Any samples or loops I use are pretty well recorded so I just use the faders to balance them
When it comes to mixing I tend to get a nice bass level on the master channel (-9db) and then add the drums, vocal, other instruments - balancing the faders to keep the master bus bouncing around the -6db level
As it is my own stuff the lines between recording, producing, arranging and mixing get a little blurred
This has helped me get in to the habit of turning things down rather than up
If I am doing a mix for someone else I take a slightly different, more disciplined, approach as I sometimes don't know what I am going to get and I kinda specialise in mixing for those that aren't used to proper recording as well as seasoned pros
I will load up their tracks into SONAR and then balance things out using the gain pots at the top of the channel to get all tracks bouncing around the same point with the faders set to 0
I will then mix using the faders, knowing I can tweak the gain if I need to, using the principles above
I leave the final polish and volume boosting to the mastering process