Having a consistent configuration will be a big help. I'd suggest making small changes, one at a time.
If you have access to a pool, take advantage. Get in the pool and get horizontal on the bottom. Add gas to your wing a little at a time until you just rise with a deep breath, and fall when you exhale.
Having the bottom as a reference will give you some feedback on trim. If your knees hit the bottom first you either have dropped your knees, or you are a bit head up.
Try swimming as close to the bottom as you can without touching.
Good luck, have fun. Let me know if I can answer any questions.
Tobin