Sissy Squats and don't lock out. Knee dominant as opposed to hip dominant (this applies to Squats). Try squatting with elevated heels, DON'T push your hips back too much, let the knees travel forward some, keep the torso upright and don't lock out. This might mean using less weight. You could also do Hack Squats. I've found Charles Poliquin's material on this very topic to quite helpful.