Repetitive Strain Injury from typing is a complete bastard if you are self-employed in a role that demands that you write. I’ve learned to live with it, so, for the benefit of posterity and @amandita, here are some top tips:

• Apparently posture is important, but it doesn’t seem to make much difference to me because my problems are in my hands and wrists. If you get back or neck pain, though, read this.
• Wrist rests actually seem to make things worse, possibly because they force me to stretch out the backs of my hands and put pressure on the undersides of my wrists.
• Lots of problems can be solved by ditching a mouse and using a pen tablet. Wacom is the best brand. They are much more natural than mice, and don’t force your wrist into an unnatural position or put pressure on the back of your hands when you click. Plus you can use handwriting recognition software, which is fun and oddly therapeutic, but slower than typing.
• Get a new keyboard. As keyboards age, some keys get sticky and need more pressure to depress, even though you don’t notice it. A really sinner is the <ENTER> key, which you usually go for with the (weak) fourth finger of your right hand. I always choose soft keyboards (laptops are best, but the new Apple standalone keyboards are excellent) and try to change them at least once a year.
• If you’ve been on the lash the night before, rehydrate.
• RSI tends to feel better after exercise, presumably because the blood gets moving through the effected parts once more. Get out on your bike.
• Lots of people swear by microbreaks and stretching exercises, though they don’t seem to make much difference to me.
• Use your hands in different ways. I play the piano, but you can also knead bread etc. Guitar makes it worse.
• Think twice about speech recognition. I’ve yet to find software that really performs.

If I had to choose one single thing that had made the biggest difference, it would be the pen tablet - even though, bizarrely,  strain from use of the mouse should only affect my right hand.