Did you know that the hardest part of your squat is the moment you are at the very bottom of the movement trying to push back up to standing. It requires the most work from you and the best way to help you out with this exercise is to target your hamstrings and glutes, making them stronger will allow you to work harder. How? Well, the way you target your hamstrings and glutes in a squat movement is to focus on more of the movement at the very bottom.
So either hop onto a smith machine or hack squat and focus all attention in repetitions at the very bottom of the squat. Squat to the bottom and then only return halfway and back down again. Perform sets of this with a reasonable weight over a 3-4 week program and you will find your squat is stronger!!