In dressage I like to have a straight line going the entire way down the body www.classicaldressage.uk
explains it ion an easy way.
Jumpin should be the rear raised slightly out of the saddle with all the weight in the legs not in the hands which will thrust you foreward. A slight tilt in the hips allows you to adjust your position in accordance to the the jump. Don't hang on the reins or fling yourself up the neck its not pretty!
To give a horse your heart guarantees a love that will last forever undamageable