I would stress varied exercises. Push-ups are known to exert stress on wrists, you need to do a variety of heavy lifting exercises (if you already have RSI, start gradually and watch YouTube videos how to do it right)

Also, stretch your arms.

For me, this book was a God-send:

https://www.amazon.com/Repetitive-Strain-Injury-Computer-Use...

I had pretty serious RSI issues a few years ago. Thanks to this book (and working out), I forgot all about it - you can do it, too!

Three more resources:

http://web.eecs.umich.edu/~cscott/rsi.html

http://www.rsipain.com/

http://www.amazon.com/Repetitive-Strain-Injury-Computer-User...

I used to have very bad RSI, and two things saved me: 1) this book: http://www.amazon.com/Repetitive-Strain-Injury-Computer-User..., and 2) this doctor: http://www.yelp.com/biz/mehaffy-rick-dc-redwood-city (only helpful if you live in the Bay Area). Good luck.