Start to think about jump throughs/backs as an arm balance: hands, arms, shoulder girdle. Your hands support your body weight. Spread your fingers wide, press down through your knuckles, and keep your arms strong, which should all help to engage the shoulder girdle. You must learn to balance while shoulders are forwards of the wrists.
Turn on your core! This is linked to creating length in your arms (students often complain to me that their arms are too short to jump through): from downward dog, go into Cat pose (Marjariasana) in preparation for jumping through: curve your spine, lift abdominals towards the ceiling (enabling scapula protraction). Keeping that shape and lift, take the knees off the ground and jump through.
Legs need to work. Draw your knees and feet as close to your body as you can, (which will mean curving into a tight ball shape). In preparation for jumping back, make this shape with the feet off the ground and hands forwards of the hips/shoulders forwards of the wrists, before lifting up. For jumping through, go into this shape as soon as you jump.
Gaze helps keep your body in the right place. When jumping through and back, keep your head up (chin lifted) and gaze forwards to the front of your mat, even when lifting the knees off in the Marjariasana preparation. This creates a counterbalance and will stop you falling forwards.
Once you get the technique, it’s just a matter of persevering and persisting with it every time you jump through. Little by little, your jump throughs/backs will start to feel more fluid and less challenging.