Sidespin loops
Do you loop with sidespin? If not, why not? There's a common misconception that a loop should be 100% topspin. It's often more natural to loop with some sidespin, as the shoulder is normally higher than ball contact, and so the arm is naturally tilted slightly down at contact, meaning contact would be a bit on the far side of the ball, thereby creating some sidespin. (Some coaches recommend loops have about 15% sidespin.) Or you can create sidespin intentionally by simply dropping the wrist to hook the ball so it breaks left, or raising the wrist so it breaks right. (Lefties should reverse.)
It's not only more natural to loop with some sidespin, it's probably more effective. The sidespin makes the ball curve in the air, jump on the table, and jump sideways off the opponent's racket, giving him great difficulty. Plus the very curving of the ball over the table means it stays over the table a split second longer, giving it more time to drop and actually hit the table, thereby increasing consistency. (At least that's the theory I've been told; more sidespin means less topspin pulling the ball down, so it's a tradeoff.)
When looping from the wide forehand it's especially natural to loop with sidespin as you drop the wrist and hook the ball back to the table, with the ball curving to the left (if looped by a right-hander). When looping from the backhand corner with the forehand you might use less, as you are now contacting the ball on the near side - and now, in fact, may sidespin the other way, so the ball jumps away to the right (if looped by a right-hander). This latter type of sidespin is generally more difficult.
You should generally loop either with whatever sidespin is most natural (without forcing it), or intentionally use sidespin to mess up the opponent (which is why many top players learn to sidespin either way, usually so that the ball breaks away from the opponent).