Taking frequent breaks, alternating to a standing desk, ergonomic everything has made my awful RSI go away almost completely.
Most important was breaks and not using a laptop keyboard/trackpad while sitting down in a chair, ever, for a long period of time. That causes insta-RSI for me.
I was using WorkRave to prompt me to take breaks. Paradoxically, this made things worse as I was getting more stressed about getting back to getting stuff done during the break. The key is to internalize and accept that you need to take breaks, and to relax during them.
Edit: particularly #14 in computer_desk_stretches.pdf
Most important was breaks and not using a laptop keyboard/trackpad while sitting down in a chair, ever, for a long period of time. That causes insta-RSI for me.