grubbys might be the pick of the moves to learn if you want to also learn to do forwards. many of them end up a bit forward-esque when you jump too high or go too far down wind
flaka took me the longest to learn to do so far and i'm only consistent in the one direction. I didn't have any risk of board damage, but i've put a lot of holes and marks at the lower part of the sail becuase of landing hook first on the sail and skidding across it
and as barn said, shaka is also tricky. Even after 5 weeks worth of
constantly trying them literally every day, i'm stuck at "half shakas" with just the occasional hint of getting right around

and had some really bizarre contorted stacks
i too agree with duck gybes as the good next move to learn, then loops, vulcans, spocks, grubbys, flaka etc.
i want to be 21 again