The move from lying to standing on the board — one single flowing motion while the wave already carries you.
The pop-up decides half your session, and nearly everyone makes the same mistake: standing up in two stages, knees first, then feet. That costs the split second in which the wave rolls past. It should be one motion — hands under your chest at lower-rib height, press the torso up, then pull both feet under your body in a single sweep and land in a low stance, eyes already where you want to go. The second big error is looking down at the board: you go where you look. Practising dry on a towel does more for this than another session in the water.