The first and best step to minimize the chance of injury from falling is to simply not put yourself in situations where you are likely to fall…Deep water, excessively slippery rocks, big flat slab bottom style rocks, heavy current, etc.
That said, once you realize you’re in a bad spot and you’re gonna fall, step one is let go of the rod, or anything else in your hand at the time. It’s better for both you (frees up your hands to brace your fall with) and there’s less likely a chance to break your rod by dropping it, than by landing with your weight on it. I often half toss the rod clear away from me if I know I’m going down.
Next, try to just essentially sit down and land on your butt if you can. What it’s there for and the area on you that has the most padding. Not always possible, depending on your orientation when you fall, but your butt, if possible, is the best thing to land on.
Once you do go down make sure you get up with solid footing. Falling once and being wet, is better than falling twice and being wet.
Most of my falls occur in shallow, relatively benign water near the bank, where I’m not really paying that much attention to my footing. The most common denominator in my falls are they most often involve largeish rocks (the size of your boot or bigger) that slope ever so slightly away from you. Just subtly, and not enough that you really notice it, and avoid them. Your lead foot goes down on one of those and slides forward away from you, and you’re going down, no way to stop it.