In the snatch, a cue that has really helped me is to think “Jump!” as soon as the bar passes my knees. I’m learning to completely ‘let go’ and succumb to the bar by actually jumping*. When I think and execute the lift by actually jumping (rather than perhaps focusing on the arms drawing the bar close), my legs automatically end up doing the work. When you jump, your glutes and quads contract (which is what you want) and your body goes straight up (and so does the bar – which is what you want!).
Don’t be afraid – actually jump* and see what happens!
I also find this cue useful when I’m driving on the jerk.
*you won’t actually ‘take off’ when there is a heavy weight on you but you can still mimic the movement