Set up with the bar midfoot, first of all - your full foot, including heel, so check from above and from the sides that the bar is on the actual midfoot.
Without moving it, simply bend your back, reach down and grab the bar. Push your knees forward until shins meet the bar, make a proud chest while straightening your back into a neutral line, look forward and down and PUSH.
Don't pull, push with your legs as if you wanted to push the floor away from you. If you think about pulling, you start immediatly using your back.
You want to PUSH with your legs until the bar reaches your knees, then when it happens open your hips forward as if you had to put your dick inside the bar with violence. Just be careful not to hyperextend by leaning too far back with your torso.
That's it, get used to the initial setup, then the only cues you need are: proud chest - push floor away - dick in bar - proud chest, in this order.
As for pulling yourself under the bar: when you setup with the bar above your midfoot and you bend down to grab it, ok? Instead of just grabbing it, pull the bar upwards (WITHOUT MOVING IT), you will see it bending a bit, that's taking the slack out of the bar. Sets it up for the initial movements and helps you by activating your lats.
So you grab it, pull it upwards without moving it and bend your knees until shins touch the bar. Proud chest, look forward and down.
You should feel tension in your whole body, it means you're ready and in optimal position to start.