I've been doing this long enough to know two things about mastering: first, a new set of ears on a project is INVALUABLE, and if those are experienced, intelligent ears, you're in the money. Second, people who have a lot of experience on this board just about all say the same thing: it's really dumb to master your own stuff. I believe 'em.
But I don't have enough money to pay somebody to master for me. So I just get the mixes as good as I can, and then adjust song levels relative to each other on the album. That's as far as I go with 'home mastering'. But another thing I do when I'm still at the recording and arranging and mixing stages is to use similar instruments, similar mics, similar reverbs - it helps to produce an overall sound that tends to hang together all by itself, without any other adjustments.