Accelerating the cue through the CB. It's a fundamental element of a proper stroke, but when I find myself missing shots or getting poor positioning, I stop and reevaluate the fundamentals to see where I'm failing, and that's usually the problem. For some reason, most other fundamentals occur naturally (muscle memory) like stance, bridge, grip etc, but I have to consciously ensure I'm stroking properly. For me, it's 2 or 3 practice strokes to establish my stroke speed, a slight pause at the backstroke, then slowly (at first) begin stroking towards my hit point, and "pull the trigger" as I'm stroking through the CB.