Balance boards have definitely helped me. You can buy one or if you have a skateboard deck laying around and a sturdy water bottle that works perfectly fine too. Even if you spend 5-10 minutes a day messing around on it it’ll definitely help your balance and the muscles involved with stability in your knees
Insert finger into belly button. Balance skill level instantly goes up 10pts. Plus it keeps you from flapping like a bird when your trying to lock on to that rail
one balancing exercise you can try is strapping two wooden planks to each of your feet and sliding on a long metal surface. The key is to try to stay as centered and balanced as possible.
Skateboarding in transition is by far the best thing you can do for your rail balance. Its honestly crazy how similar it is balancing on a skateboard and balancing on a rail with skis.
But if skateboarding isn't your jam, balance boards, slacklining, rollerblading, or even yoga can help