Serious Cat has some good tips. If it hurts to do squats a bad hurt not a im just sore hurt dont do them probably doin more bad then good. I like to power lift even then i Just try to make sure i can squat more then i bench and dont get crazy with it.
If squats hurt your knees (I can sympathize) try doing a roman chair/wall sit: How To: Wall-Sit - YouTube
Or dumbbell lunges: Dumbbell Lunge - YouTube