1) Posture. You want your eyes to be on the same plane as your screen so your back and neck are straight. You want your elbows to be be bent at around a 90-degree angle--that helps keep your wrists straight. And you want your shoulders to be relaxed, not hunched.
2) Breaks. Both long and short. I used to use software for this, specifically AntiRSI for Mac. I think I did an 8 minute break every 52 minutes and a 30 second break 5 minutes or so. Now that I've built up better habits I don't use this software anymore.
3) A good chair. My favorite is the Swopper. It's quite expensive, though--around $600 I think. Right now I have standing desk and no chair. I like this set up even better than sitting on an ergonomic chair.
4) A good keyboard. I like "clicky" keyboards in the vein of the old IBM Model M. I use a DAS Keyboard. Costs around $100. It's not ergonomic per se, but the mechanical keyswitches provide great feedback so you can reduce your keystroke pressure to just the right level.
5) Physical therapy aids. I use Theraputty during my microbreaks. It's like silly putty, only it comes in various levels of resistance. I like green, which is medium-firm. Costs like $5 on Amazon. Some people also use the colored rubber bands, but that's more for elbow and shoulder work and my RSI is all in the wrist/hand.
6) Other activities. Rock climbing has very nearly cured my RSI. When I climb regularly my hands, wrists, and forearms are strong enough that keyboarding can't touch them.
I suspect fighting RSI is like fighting obesity (though I only have the former so I can't be sure): it's all about building good habits. There's no magic bullet and you can't simply cure it and be done. It's an always on-going process. Hope this helps. Good luck!