from one student to another.....
aside from visualizing and going over the dive flow many times on the ground and in your head. The best advice my instructors gave me was:
right after checking out with instructor
1)focus on the horizon (or wing of plain depending on exit)
2)take a long deep breath and let out slowly to relax 3) count off and jump.......
but most importantly....arch, wave, reach, pull, arch...have fun and smile.