What I'm doing squat-wise is rocking my weight back slightly into my heels so I make sure I'm pushing up through the middle of my feet. (Doing them barefoot helps me tell where my weight is resting). I go down far enough that I feel my glutes engage, but not so far that I'm in danger of not being able to get back up again.
I don't think I'm squatting parallel yet but I'm trying to get as deep as I can without fully falling back on my ass. Maybe the weights I'm using are too heavy though.