[blacktail]

You could try a three finger under release(3 fingers under the arrow)and anchor with your index finger at the corner of your mouth.
This is what I use and I get a much cleaner arrow release.I also anchor on my eye tooth near the front of my mouth and get a consistent anchor point every time.
You will find as you tire your form will go all to heck and you will either overdraw or under draw.
When you come to full draw and hold try to envision squeezing a tennis ball between your shoulder blades and hold the bow at full draw with your back muscles and not the shoulder muscles.

To practice form get about ten feet in front of a target and close your eyes.Come to full draw and concentrate on good form and release the arrow.
When you can accomplish good form open the eyes up and step back and start shooting
What this does is eliminates one step that now becomes second nature when you shoot and you have one less thing to concentrate on when trying to learn the process of instinctive shooting.