Sometimes you just have to face things head on...
I used to absolutely hate heights. They freaked me out going up, they freaked me out moving around up there, and they freaked me out on the way down until my feet were on solid ground. Well, I ended up with a job that occasionally requires me to work at heights so I figured it was as good a time as any to get over it. A buddy of mine suggested something, rock climbing. We found a little indoor rock climbing spot to try out. Between the training, the ropes, the harnesses and the giant cushions on the floor; it was safe as can be. Even being tied to a wall with a big cushion under me, it still freaked me out. I pushed myself up a bit... and when it was time to let go of the wall to go down (barely 10 feet up) it felt entirely wrong. I'm not too sure how else to describe it other than to say it felt wrong, every part of you screams 'no!'. Eventually I had to force my hands open and let it happen. The rope caught me like it should, everything was fine. Of course I certainly wasn't cured right then and there, we spent the next few hours climbing and getting progressively higher and getting a little better at letting go of the wall to get down. It took time before I trusted the rope to catch me but by the end, we were actually having fun and ended up making it out every week to go climbing.
I realize that rock climbing and diving are different, at the very least they
usually happen in opposite directions, but the process is the same. I found that the first part is mind over matter, just face the water, grab your gear as you were trained to and jump in. The other part is to repeat the jump over and over to get yourself used to it. I'm not sure if the fear ever completely goes away, but it certainly subsides. My circumstances were a little different. I had motivation to do this to keep a job which really had no alternative to being at height. For diving, any place that you can jump into the water, will usually have a ladder, stairs, ramp, or some alternative to get you in and out of the water.
At this point, I prefer to jump in than walk in. Shore entries around here have you walking over those darn ankle-twisters people call rocks on land, and very smooth slippery ones in the water. Shore dives with walls to jump in on all have ramps/ladders but around here can have sharp little critters clinging on, I try to avoid using them as much as is reasonable.
Now if you'll excuse me, I'm off to take a long walk off a short pier