I’ll pitch in with a slight twist. There’s simply no way I can comment knowledgeably on how to crash. But you can do a few things to turn situations that other people consider “guaranteed crashes” into “saves” or at least “could have been a lot worse”. There’s actually a swath of scenarios that would cause a poor bike handler to go down and a good one to stay upright.
1) wheel overlapping or wheel chopping. For races and group rides, I would say this is by far the most common type of crash. I’m not gonna say you’ll be able to stay upright 100% of the time this happens, but you can get very close. Go to a beach or grassy lot and practice getting your wheel chopped. Don’t go too fast, of course. As long as you learn to steer away from the other guy’s wheel, you can save it.
2) HARD braking. Calibrate your hands/butt so that you let off the brake when you feel the rear wheel lift. Practice lifting the rear wheel with your weight all the way back. If you can brake this hard, and *then* crash, you’ll be a lot better off than if you immediately lock up and go OTB (one of the worst kinds of crashes in terms of breaking bones) or don’t brake very hard at all. An SUV turned across the road and nearly hit me head on. I slammed my brakes just hard enough to endo, but not to go OTB. Ended up tapping his front bumper (he stopped) and staying upright.
3) Get pushed around. Hard. You and a friend should go to a parking lot and get rough with each other. Try shoving each other, pushing their bars, pulling their shoulders etc. Ride side by side with someone, with one arm each on the other’s shoulder, clanging bars. I once hooked bars with someone midcorner in a crit. He pulled away from me and threw me deeper into the corner. But I stayed cool and upright by pulling away.
4) Brakes are death. Get really sticky tires, and I can promise you that, on a descent, the safer thing to do is almost always to lean it out. Grabbing a panicky handful of brakes midcorner is a recipe for disaster because of how instantly you can overwhelm the tire. It’s much more gradual of a fall (or even a nonexistent one) if you let Jesus take the wheel and lean.
5) Reinforce yourself. Unless you have huge ambitions, most cyclists can stand to gain some muscle/tendon/bone/ligament density. You don’t have to get huge. Just do high impact and high load exercises in very small volumes. This isn’t just a crash thing. It’s better for your overall health. Many people injure themselves doing mundane stuff, especially as they get older. Being flexible and strong will reduce the probability of a serious debilitating injury and will also expedite your recovery.
Feel free to disagree with me. Hopefully this isn’t too off topic.