Visualize. You don’t want to advance forward on the kip, you want to remain in the same relative position you start in. Focus on getting your body into as much of a reverse “U” shape as possible. No back flexibility? That might be a problem. Start bridging.
Don’t let your hips collapse downward (i.e. lose the reverse “U” shape) at any point during the movement. The force of the hips/pelvis driving upwards is going to drag the rest of your body along with. Picture a rope tied around your waist which pulls the body upwards as you execute.
Use stretch-shortening as well. Swing your legs back quickly in order to explode back up more violently.
The kip is really simple. Once you actually nail it, which you most certainly will with practice, you’ll wonder how you ever failed to do it. I no longer have much need to kip, haven’t trained the kip in years, yet I can easily do a no-hand kip on demand. You just need a base level of strength (which almost every non-fatty already has). Beyond that, it’s just proper technique.