From what I understand, the timing of the crouch input relative to when you jump is the main thing that can fuck up a random powerbounce, because if you press crouch too early, the only thing you can get out of it is a random crouch bounce. But if you press it too late you might bhop and get hit by the rocket before being actually crouched.
What I would recommend to get comfortable with the key presses is to just practice in a place with a setup before going for random ones. Once you're pretty consistent with a setup, go try to hit some random ones after starting a pogo (maybe use a tp bind to speed things up). If you're not hitting anything for a while, go back to the setup to see if you're still using the right key presses.
One thing that sucks with random powerbounces is that most of the time it's impossible to troubleshoot what went wrong. Was your key input wrong or were you just not at a bhop height? The only thing you can tell is if you don't get teleported and get to try again, you did the jump/shoot/crouch too early.
I noticed that for me, the correct timing to do the jump/shoot/crouch was a lot later than I first thought. If you get a lot of second chances in a single attempt you are most likely pressing things way too early. If you get teleported a lot on your first attempt you are probably too late.
Edit: if things are still really not working, try going just for a bhop see if you are at least timing that part well. A powerbounce is just a bhop quickly followed by taking rocket blast while crouched.