The first thing is that you have to get up a lot quicker on a steeper wave, then STAY LOW.
If you stand all the way up you have less balance. On fast, steep waves, everything needs to be so much quicker, so get to your feet but stay well crouched as you go into the drop.
Positioning is important in getting barrels, you need to get yourself just to the side of where the barrel is going to break so that you can drop and turn under the lip as it pitches over you.
I've only ever caught one in a standing position and I think that was more luck than judgement.