An efficient squatter is using his glutes to extend his hips not his hamstrings. The reason for this is that the hamstrings have two functions: extending the hips and flexing the knee (the hamstrings crosses both the hip and knee joint). If you use the hamstrings to extend the hips you also get a flexing torque at the knee. This means that the quads have to work even harder.(1)
However I think it may be a problem for some people that their glutes are very weak, in which case they will tend to use the hamstrings even if this is inefficient.
If this is the case one should focus on taking a wide stance and hitting full depth (2). In the bottom position of the squat the knee is flexed which results in less tension in the hamstrings. It is therefore difficult for the hamstrings to contribute to hip extension and the glutes will therefore contribute more in the bottom position of the squat.
(1) Hamstrings–The Most Overrated Muscle Group for the Squat
(2) Squats Don’t Work Your Glutes (Because You’re Squatting Wrong)