If you're serious about improving your squat mechanics and how to squat more weight then you need to watch this video.
There is also a nice accessory exercise at the end. This is used to cue the mechanics with a lighter weight. Also without having to put a heavy bar on your bar. His main cue here is to let the knees come forward keep them forward as you drive up.
main cues to take away are:
1. keeping the weight in the mid foot. toes down. (between to big toes and the heel)
- far too often are people cued to push their weight back on their heels. yes your heel should be in contact with the ground but you this creates a shift in balance which causes you to excessively lean forward if you don't have good ankle and hip mobility.
2. Look forwards.
- not up. not down. straight ahead. again this helps you stay inline and more upright in the squat.
3. knees come forward over the toes.
- by allowing your knees to track forward and over the toes this always for a more upright body position.