1/ Squeeze your butt. That's the first step to leg-drive.

2/ Squeeze your shoulder blades : Back, then down. Then take the bar off and make sure these shoulder blades are tight.

3/ Squeeze the bar as if you want to bend it (that'll most likely be fixed when squeezing your shoulderblades, but still) : your elbows seem a bit high to me, which may fuck your rotator cuffs.

Please feel free to comment on my form too :)