Cues to help you clean up your squat form: (if this is helpful, let me know and I'll post more tips for other exercises).
Squats: Major cue-"Feel your heels" at the top & bottom of the movement. Keeping the weight in your heels shifts your center of gravity back so that you feel it in your glutes and hamstrings. We don't want you feeling it in your knees.
When you set up for your squat, first set your body up from the feet up and run through a mental checklist every time. Check the feet (should be pointing straight ahead or slightly out), feet width determined by type of squat but start just slightly outside hip width, core braced, initiate movement by shifting hips back (think push the tush back) and lower with a tight core and drive up through the heels while squeezing the glutes. Look straight ahead: squatting in front of a mirror is important so you can be visually aware of your form. Gym mirrors aren't about vanity. Get comfortable lifting in front of mirrors to monitor form. Don't look down at your feet because your body will follow your eyes. To maintain proper posture, look straight ahead.
Another key cue is to "spread the floor"-imagine your feet are bolted down but you're trying to spread the floor apart with your feet (keeps the pressure on the outside of the feet and helps prevent knee caving).
Never let go of your core: stay braced for a belly punch!
Inhale down, exhale up.
Not quite ready for Barbell squats? Squat variations to try: goblet squats or the double kettlebell front squat