if it's jumping, you probably have an old bur and need to replace it.
you also might be slowing down the high speed bur too much...that handpiece is built to spin fast...if you want to go slower, switch to the slow speed for now.
i suggest getting the general form with the high speed handpiece at high speed and then refining it with the slow speed handpiece. You can knock out the unsupported enamel with a hand instrument.
right now, you're learning fine motor technique and that just takes practice...trial and error...
make sure you have the mannequin's body adjusted to your height and its neck angled appropriately for either direct or indirect vision...get some good loupes (>3.5x) and become comfortable with your mirror. Don't hold your handpiece too tightly or else you'll lose all fine motor capability. I found it best to have index, thumb and lateral portion of middle finger pads on the handpiece so that I can feel the vibrations and fine touch as much as possible. i rest the handpiece on my middle finger and "pinch" the handpiece with my index and thumb at opposite ends...my fingers form a three pronged pincer. my grip is relatively close to the handpiece's head similar to how you would hold a pencil grip.
the speed at which you move your bur is going to determine whether your outline will be jagged or smooth. If you go too slow, it'll be jagged but if you go too fast, it'll be harder to control. I think the speed at which you should move the bur is close to the speed at which you would put contacts on your eye. lol
