[MilnerRoute]

I try to make sure I have the best equipment. (So a comfy ergonomic keyboard, and a good mouse.) When my hands started hurting with one mouse, I switched to a different one. (Basically, just using a different set of muscles for mouse clicks.)

But maybe that's the most important thing: paying attention to your body, and if it hurts, stop, and try to figure out what you're doing. (90% of the time it's a posture thing -- so I can solve it by not sitting in that particular posture.)

If you don't sleep well, you can end up slumping in a bad position which leads to arm pain. So: sleep well. Make sure you eat enough and have enough muscles built up to sustain a healthy posture. Things like that.