Here's a lifting tip.
If you always find yourself struggling to keep your butt from flying up, try to start with weight slightly further towards the toe.
This should enable you to use the quads and not shift the knees and hips back and tighten the hamstrings, and then fail to get back to the center when the bar passes the knee.
We've noticed that a lot of people like to shift their weight into the back of the foot, and have the bum rise up first, thus tightening the hamstrings. It becomes more of a "muscle" driven lift, that a movement driven lift. The first pull becomes stronger, at the expense of the second pull.
We like seeing movement driven lifters, not muscle driven lifters.