rotate your hips!

There has to be sufficient friction so you can hit the ball thinly without it slipping.
It must be elastic, so you can "load up" the spin by stretching it sideways. This stretching is a combination of sponge "skew", pip bending and topsheet stretching. Thicker sponge means you can load it up more.

Generally, softer rubbers work better with long swing, while firm rubbers favor more compact strokes. The principle is much like loading up a slingshot. With a soft rubber band you need to stretch it more for a good shot. With a firm band you don't pull as far back, but must use more force when stretching.

Yeah, this is where I think it gets complicated.
My coach told me not to rotate my hips too much because he said before that I was wasting too much of my energy moving by rotating my hips. He wanted me to use more of my forearm and arm to generate the power.... But it's so awkward doing that. Maybe I need to find that right balance between moving my hips and arm.

I think your final sentence is what your coach wants. If not, get rid of him because you'll end up with injuries if all the power needs to come from your arm and forearm.

A loop is a smooth motion of energy transfer starting from the bending of legs, going over the rotating hips and upper body and ending with the arm, forearm and wrist. Most of the power comes from the legs and the rotation. The wrist is to finetune the movement. All these components are necessary to have a good loop.

+1 very good post.

You will wreck your shoulder if your power comes mainly from your arm. What level is your coach?

About the question in your sig: Does the rubber matter? Yes it does, to some degree. More for looping than for any other stroke, I think.

So what do you need in a rubber?
There has to be sufficient friction so you can hit the ball thinly without it slipping.
It must be elastic, so you can "load up" the spin by stretching it sideways. This stretching is a combination of sponge "skew", pip bending and topsheet stretching. Thicker sponge means you can load it up more.

Generally, softer rubbers work better with long swing, while firm rubbers favor more compact strokes. The principle is much like loading up a slingshot. With a soft rubber band you need to stretch it more for a good shot. With a firm band you don't pull as far back, but must use more force when stretching.

Does your "generic" rubber have a name?

Elaborating THC's advice: To enable hip rotation, you need to lean forward, so your weight rests on the front half of your foot. When your heels are free to move sideways, your hips are free to rotate. If you move your weight backwards, that locks up your heels, and rotation is only possible from the waist up.

Thanks everyone for your tips!

My coach is 2200. Maybe I should find a 2500 level coach because it sounds like he is messing me up a little bit with his teaching.

I think you should probably listen to your coach, and if you don't understand why you are doing something just ask for an explanation. Asking your coach questions is generally a good practice.

Often times (less nowadays) I am learning something new from my coach and I just dont understand why I am learning a certain stroke, or why it is better, or how it even fits in my game because I never do it, or a variety things. Or he is trying to show me a stroke that when doing my own way works, but when I am trying to learn the proper form I just fail miserably. Then after 3 months of sucking at something all of a sudden it clicks, and I can begin to understand why I needed to do it this way and why what I was doing was so wrong, my doubts were washed away.

Doubting something you don't understand is natural. Perhaps your coach is still trying to teach you building blocks and fundamentals before you go into full fledged power looping. If you like your coach and he has helped other players and you genuinely think he can help your game. I would follow his direction.

A coach rated 2200 knows this.