This took me a while to get the hang of. My struggle was everytime I was on the throttle, I'd come up nose high - and sometimes end up on the ground. But I wasn't
getting anywhere - I couldn't jump far in third gear because I wasn't on the gas - because I would loop out.
The biggest tip I got to help me learn how to jump right was this: when you jump, you should be forward enough to look right down your number plate. This keeps your weight far enought forward so you can carry the thottle on through the whole jump.
But ... this comes with the following warning: now you
have to be on the gas when going up the jump, because if you let off a little (like I always did), you'll endo. Did that a couple times, too... It's best to learn on a big step-up. It finally got me comfortabale enought to do it elsewhere, while at the same time saved me from many loop-outs and endos.
Take a look at this pic, you'll see what I'm talking about... and good luck!