Mine was pretty bad, in hands/elbows. Here is what fixed it for me. I don't have the pain much anymore, but I have to keep up with the following. For context, I'm in my late 20s and still code around 12hrs a day.
Note: nothing expensive. Also, what works for you will vary.
1. Bad posture in back/neck could noticeably make my hands numb. Got a strap on thing that helps remind me to sit straight.
2. I think my hands/arm muscles were very weak, and somehow that made things worse. This kind of thing helped A LOT:
https://www.amazon.com/TOCO-FREIDO-Strengthener-Adjustable-R...
It hurt a little at first, but after the first couple days things felt noticeably better with a tool like this. Note - I'm not a doctor, don't injur yourself...
3. To help posture, a little stand to put my feet on. This does wonders.
4. Sustainable schedule. I don't touch a keyboard on Saturdays, or Thursday nights.
5. Eight hours of sleep to let the body heal. Disciplined sleep schedule.
6. Games like CSGO are really bad contributors to RSI, so I cut down time on this (only couple games a week).
7. For some reason, stressful or work I hate doing makes RSI MUCH worse. So, try put yourself in a position to do things you enjoy.
8. Split keyboard. Stationary ball mouse. The mouse is a big one.
9. Monitor AT EYE LEVEL and close to you. I had my monitor far away with like 13px font like everyone else. This meant I was leaning, ruining my neck, and pinching/straining nerves.
10. Look at piano players. They float their arms. Everyone suggests resting your arms flat on your arm wrests. This seemed to cause a pain to go up my arms and into my wrists. Typing with floating arms feels much better, but I have to switch it up to prevent strain.
All in all, it's a bunch of little stuff I was doing wrong for a long time, and I caught up with me. I hope someone finds this helpful. I did get a nice chair, but this didn't seem to help much, so I didn't list it.
If I go back to a laptop, the pain comes back in a day, so I try to avoid that.