Before they ever touch a weight, I always advise clients and friends to master movements with just their bodyweight. Before jumping into a 175-pound barbell back squat you should be able to perform a perfect air squat. Once you've mastered that move, begin to add weight. Regardless of how much weight you add, the goal is to be able to execute a squat with proper mechanics.
A sign you're lifting too heavy is being unable to perform a squat with good mechanics, which is sitting back with your weight in your heels, maintaining a flat back and your thighs parallel to the floor. Another physical sign that the weight is likely too heavy is straining. We've all seen a person in the gym trying to lift a heavy weight turn red as a tomato from lack of breathing. While weightlifting shouldn't feel relaxing, it also shouldn't make you feel like you're about to pass out or pull a muscle.
