It is so easy to get caught up in a project and not realize that your fingers, wrist, back or eyes ache. And when you finally stop, you ask yourself, "what was I thinking!?" Today's tip: build break times into your pattern. I always make a photocopy of my patterns and then write all over them as I work my project. This also makes it easy to set break times within the pattern. Just write it in every 10 or so rows. You know your pattern and speed, so you decide how often.
At break time, get up and walk around. Do some finger aerobics, like alternating making a fist and spreading your fingers into a flat hand or make the sign language sign for "flash" repeatedly. Maybe some jumping jacks to get the blood flowing again. Certainly stretch out those tight places.
Eye strain can be a common nusance. Combat this by looking at things that are different distances away. Your crochet is rather close to you so look at something far away and then at something half that distance away. Vary the order that you look at those things and for how long. Allow your eyes to adjust to each distance. Think "eye aerobics."
Find out what works best for you during those break times. Your body will be less stressed from the constant repetition of crochet movements and you'll be able to crochet for longer periods of time.