I tend to do it in front of a mirror to be able to watch my form.
I get my thighs horizontal with the floor (so 90 degrees heh)
and I try to keep by back as straight as possible by arching my shoulder blades in.
Im very inflexible mind you and have to lower my torso quite low (bent over towards crotch area, but spine still as straight as i can possibly make it) in order to achieve the 90 degree mark.
still seems the only place I notice a burn are my abs (sometimes) when I push up to standing position again.
EDIT: Does anyone think its worth PAYING to goto a gym for a month to learn proper form? Im really shy and get anxiety attacks when I think about going to a gym.
I think I just need to make friends with someone who enjoys answering my stupid lame questions, and actually knows what they are doing. BLEHHH (heh)