Technique in the squat is critical, so you will want to practice squatting frequently. Look to improve your form on the squat before you look to fix a particular weakness. What many people consider to be a muscular weakness is often an imperfection in their technique.
With that said, most raw lifters are still going to be weakest right out of the hole. Here are two exercises to help improve strength out of the hole.
When doing pin squats, place the safety pins so that when you are just above parallel in the squat, the barbell is resting on them. Squat down to the safety pins, let the weight come to a complete stop, then squat it. The stretch reflex will be greatly diminished, removing the rebound out of the hole. I prefer beginning this movement from the top position just like you would a competition squat. It will feel more natural, and have more transference. The problem with starting this exercise from the bottom position is lifters often don’t start in their natural bottom position, thus diminishing the effectiveness of the exercise.