One extremely common error to make in the squat - intentionally or not - is to do a shallow squat.
Tony Gentilcore's article Squat Like You Mean It covers this error. It is an excellent round up of drills to get your squat deeper and alternatives to do until your squat depth gets down to where it needs to be. The alternatives, by the way, make great change-of-pace lifts and accessory lifts for the squat, too - clean grip reverse lunges, Bulgarian split-squats with extra ROM (range of motion), deadlifts . . .
Not to be left out is Jim "Smitty" Smith of Dieselcrew talking tips for attaining proper squat depth. Jim Smith's articles are always very thoughtful, so check this one out as well:
Is Depth Your Problem?
Meanwhile over on Elite FTS there is a new video series called "So You Think You Can Squat?"
Here is Part 1.
There are three sources to help you improve your back squat, whether you are a powerlifter or not, athlete or not, recreational lifter or not. Everyone has to squat down and pick things up; a back squat is just a barbell-weighted version of a basic movement pattern we use every day.