Whether or not the DB touches the shoulder also depends on the size and type of the dumbbell, as well as whether not you bend your wrist inwards at the top of the motion (as in thumb rotating towards...
A lot of times you'll see boxers almost running in place, only obviously not bringing their feet up very high at all, just enough to let the rope pass.
Somewhat ironically, when I was a lifeguard for several years and not in the shape I'm in now, I would suck in and flex my stomach pretty much all the time.
I've also found it helps if I twist my wrists OUT (as in supinate them) so that instead of the DBs being parallel with my back at the peak of the movement, they're at a diagonal.
Squat heavy for big legs. That being said, it is difficult to squat heavy if you're working out at home without the equipment necessary to squat heavy.