When I used to take parkour lessons, the first thing they taught me was how important it was to know how to fall safely. Much of the class time was spent practicing how to fall, and the techniques I learned translated extremely well to unicycling.
Not all body parts are created equal. Some are more fragile or important than others, so it's important to understand what to priotize while falling.
Your head and your brain are the most important parts of your body to protect, and can be the most dangerous to damage. All the techniques I will talk about on this page prioritize safety of your head!
While not nearly as important as your head, getting a sprained or broken wrist still sucks. Wrists can be injured very easy, and are the most commonly used body part for breaking falls if you are not experienced at falling safely.
Similarly to wrists, elbows are relatively fragile and hurt a lot when your body weight comes down on them.
Many of the techniques described below are taught in this video. I highly recommend watching it after reading this list: https://www.youtube.com/watch?v=ohjbbVwg6OU
Ok I know this sounds obvious but there's an actual piece of advice attached to this. Your first line of defense is staying on your feet for as long as you can. If you are going to fall, the damage can often be minimized by staying on your feet and trying to stumble out of the fall. Sometimes you get lucky and are able to recover fully from a good stumble!
The next best way to fall is by getting your feet under you as you lose your balance backwards, so that your legs can gently carry your butt to the ground before you roll onto your back in a controlled manner. When rolling, you must bend your back and neck, so that your head is tucked into your chest, and does not hit the ground. The slower the better! If you need to slow the backwards rotation to protect your head, you may slap your palms against the ground once you start rolling onto your back. Keep your arms straight and don't put any body weight on your arms when doing this!
If you are falling forwards and cannot stay on your feet, your best bet is to roll over your shoulder and onto your back. This skill takes some practice so I recommend watching a video to learn the proper technique. Do NOT roll straight forward over your head. This is a diagonal roll over one of your shoulders, which is done this way to protect your head. It's very important that you tuck your head into your chest during this roll to protect it. I also highly recommend practicing this roll in a safe environment with a soft surface, so that it's instinctual and your technique is good when you need to do it for real.
This roll is basically just as important as technique 3, but ranked slightly below because you can often get away with using technique 2 instead. This roll is also harder to pull off well compared to 2 and 3, and should only be done if absolutely needed, and if you've practiced it plenty in a safe environment.
The sideways roll is actually just an easier variation of the forward roll, and very similar in technique.
This is another way to fall that relies less on your feet and rolling. I also recommend looking up a video on how to do this fall. It involves slapping your palms against the ground before the rest of your body hits to lessen the impact. This type of fall should only be done if rolling is not an option.
All of the above methods (aside from the breafall in some cases) typically require controlled descent with the help of your legs. Unfortunately, it's sometimes possible for your legs to be swept away while unicycling, leaving you only with your arms to slow your fall. If this happens, you should:
Slow the fall with your hand/wrists, being careful not to take the full impact with just the wrists, and keeping your arms bent (straight arms are VERY bad)
Let your elbows hit the ground as gently as you can manage
If possible, get your feet or legs to the ground ASAP. Otherwise, absorb some of the impact with your butt, trying to avoid your tailbone as much as possible
Roll onto your back as much as possible, and ensure your head is tucked into your chest (or away from the ground if falling forwards/sideways)
The best thing you can do without your legs is attempt to spread out the impact as equally as you can to as many body parts as you can.
Obviously you don't need to get this far into the falling techniques to consider wearing a helmet, but if you think you will be falling in a way that even technique #7 can't save you from, you should definitely be wearing a helmet, and considering other ways to keep yourself safe (mats, spotters, harnesses and rope, etc.).
The goal of this page is to give you all the information you need to avoid hitting your head. Even if you are wearing a helmet, you should still avoid having to use it. Thankfully, unicycling is a surprisingly safe activity. Due to the way unicycles work, you can often step off in any direction and get at least one foot on the ground.