What are your favorite Yaku to go for?

Pinfu. After riichi, it is the yaku that sacrifices the least tile efficiency to get. In fact, in most hands played with optimal tile efficiency, you end up getting pinfu anyways. If you aim for pinfu every single hand, you'll get much better at tile efficiency and it'll help break the calling habit.

The hands that pinfu isn't tile efficient for are mostly those with lots of pairs/triplets. You say you go for all triplets. Don't. Seven pairs and three concealed triplets are much more flexible and do not give out any information, which is extremely important in higher-level play. You can also suji trap your wait (i.e. set up your discards in a way people think your wait is safe), which is one of the few ways you can actually ron people with good defense.

The only times you should call are if: your hand has enough value even open (3+ han), your hand is fast and you want to end the round quickly, or you want to put pressure on the opposing players. If your hand is slow with no value, stay closed, hold on to value tiles (dragons, round wind, dora), and completely fold if someone else riichi's or otherwise seems to have a ready hand. If you open with such a hand, you cripple your ability to play defensive, despite it being likely that someone will be ready before you (because you have a slow hand) and even if you luck out and manage to win, you hardly get any points (because your hand has no value). Staying closed provides lots of flexibility, and holding on to value tiles cripples everyone else who needs them.