First handgun I ever owned was a .45 auto. "No no", they all said. Start off with something smaller and work your way up.
I dunno what works for others, but I know what I did. I went to the range one weekend and shot hundreds upon hundreds of rounds non-stop 'till the big boom and recoil didn't faze me anymore. Literally shoot the damn thing 'till you're sick of it. Over'n over again. Like getting used to a door slamming shut 100 times a day. After awhile, it doesn't bother you. I did this and within a month or so, I was grouping 2-3" @ 25 yards with a bone-stock Series 80 Colt.
Now, years later, after not having been shooting that much, I've started flinching again. I know what to do, just haven't gotten around to finding time to spend a whole afternoon shooting 1000+ rounds. So, I do what everybody else already says. I surprise myself when the gun goes off, squeeze slowly, shoot within 5 seconds of raising the pistol etc...