Coming from another relatively new guy to the sport: The way I learned (and am still learning) to stay in place on a turn is by doing 2-way drills with lots of 360s and 540s, and instead of focusing on turning quickly, I turn fairly slowly (maybe 4 seconds for the whole turn) and keep an eye on my separation from my dive buddy the whole time. That way, instead of thinking of it as just dropping a shoulder or something, I have time to judge each small movement and the effect it has on my position. Once I practiced it a lot slowly, the speed started to come more naturally.
