I remember when I was 4 or 5, they were planning to do a bike safety thing at school. I said to my folks, "I want to learn to bike without training wheels!" so they obliged. Just outside where I grew up, there was a steady, slightly sloped grassy hill. That's pretty well how I learned to ride a bike. I'll never forget the time that I crashed into a parked car, lol! I didn't feel bad about it though; dumb maybe, but I remember when my brother did the same thing!
Getting back on a bike 3 years ago felt weird at first as I hadn't been on one since 2002. I started with doing wide, flat gravel rail trails and gradually moved into doing actual trails and just kept at it from there. I have moments where my coordination will just go out the window, but I remember on a slight uphill slope I fell over and landed in a bush! Now I had biked more complicated stuff prior, which is what made it comical! I've been lucky when it comes to wipe outs; I usually wind up landing in the local foliage. My personal best was when I was trying to keep up to the neighbor. one of my wheels slid into a rut and I superman-ed over the handlebars!
Like learning anything, start slowly and go from there; start on flat, wide surfaces; preferably soft ones. Don't worry about shifting; something easy to mid range will suffice. If you're on grass, you'll want to be in an easier gear. Once you have some momentum going, the bike becomes more stable.
Now fencing on the other hand, I suck at fencing. I enjoy it and I've made a lot of close friends through it, but I'm terrible at it. Unless it's blatantly obvious, I don't pick up on the body language and usually wind up parrying with my face!