I think I've found that for right walls, you have to press A first, then shoot. I have a bad habit of holding D too much. Part of doing those right walls is strafing hard right as part of the "shoot against the wall" element, like so:
1. Jump up near the wall, using D if necessary;
2. Turn about 90 degrees to the right;
3. Hold A;
4. Shoot in "that spot";
5. Quickly look forward again;
6. Hold D and strafe hard to the right, then start again at point #3; time from #3 to #6 is less than half a second.
It's a very speedy and precise operation. The faster you go the harder it gets.