This might sound silly, but this is what I do to conquer any fears I end up having (ranging from horses to roller coasters xD).
Step 1: Lie to myself.
"Pffft. So what if he takes off with me or bucks or something. I like it when he bucks. Yup. It doesn't bother me at all." Eventually, if I keep telling myself that, I end up believing it somehow. When I was in 8th grade, my school took a trip to the Busch Gardens. I told myself that I loved roller coasters. In reality, I'd never been on one. I also told my friend I'd be her roller coaster buddy. The pressure of having someone to own up to also stopped me from chickening out. Turns out, I hate roller coasters. I decided that after I rode every coaster in the park. But at least I conquered my fear...? xD
Step 2. Just do it. But have a game plan.
I used to have problems asking Blaze to canter because he bucked me off once and I broke my ankle. Sooo I followed step 1, and then came up with a plan. Even though I 'like it when he bucks', give him a kick / tap with a whip, and act like nothing bad happened. So then I hopped on him, confident that I love when he bucks. I got him into the trot, asked him to canter, made it a circle, and he bucked. Gave him a kick, he realized he couldn't get away with it, and then he didn't give me that problem for the rest of the day.
Step 3. Holy magicarps! I just did that!
Realize you just got over your fear. xD While usually I don't condone lying, lying to myself to assure myself I'm not afraid seems to work. Just make sure you're being SAFE when you lie to yourself. I knew that getting on a roller coaster wouldn't kill me. I also knew that Blaze was going to buck and I was going to be able to handle it now that I was expecting it. If you don't feel like you can handle a bolting horse, take a few steps back and don't try to canter for a while. Make sure you have your brakes under control before you try to accelerate. Once you're secure with walk-halt and trot-halt and you feel secure enough / you feel like you can handle the situation, then try again. Preferably with a trainer around, just like you said a few posts ago.
Sorry for rambling with seemingly crazy advice. xD
"There's no such thing as a problem horse. Just people that cause problems for horses." - Unknown