I feel that the most important thing in shooting is
consistency-- As long as your bullets always land in the same spot,
you can then slowly adjust your aim so that the spot will be where
your target is. So, during zeroing, you must take note of two
things 1) Your grouping is tight 2) Your bullets hit the target
(i.e. weapon is zeroed). IMHO, 1) is the hardest to get right-- but
once you can master 1) even after a short run (which the ATP
requires) then you should be fine. Anyway there is 4 components
that can help you--butt pressure, trigger pull, breathing and
weapon cant. Personally weapon cant is the hardest for me to get
consistent, so you gotta find out which is most difficult and
practice if possible.
Your CSM/Weapon spec should have a booklet/sheet of paper that
indicates where to aim on your target for a weapon zeroed at a
given distance (even if they don't have it, they should know and
can teach you), and how to lead moving targets. This will be very
important especially at 100 and 50 meters--go ask them for it and
you won't be disappointed.
Clean your weapon! I didn't get my marksman because I had to use
someone else's rifle for the night shoot (my LAD died) and it
IAed.
Good luck!