I generally spend 8+ hours knitting. I'm not obsessed or anything.... LOL
Exercises you can do to help... (& sorry - I'm horrible at explaining. Hope these make sense.)
At least hourly, put your knitting down & shake your hands - like you've just washed them & don't have a towel to dry them with.
Clench & unclench your fingers. Make a fist then spread your fingers out straight & away from each other as far as possible.
Put your hands in the typical prayer position & push. While pushing, lift your elbows a little so that your hands & forearms are at right angles & push a little harder.
From the prayer position, interlock your fingers & push outwards (palms would be facing away from you)
Put your fingers on a table/desk edge, bend your wrists backwards, straighten your arms & push until you feel the strain all the way up your arm.
Put your arm out straight in front of you & bend your wrist back like you are traffic cop saying "halt!") Pull your fingers back until you feel the stretch. Reverse the position & bend your wrist the other way so that your fingers point down & stretch till you feel it.
Other things that I find helpful are circular needles rather than straight. The circs keep the weight of your knitting centered in front of you rather than hanging out on the ends of the straight needles. MUCH easier on the wrists!
My carpal tunnel gets worse when I knit with heavier yarns. These days, I try not to knit with worsted or heavier for more than an hour a day. DK & lighter yarns don't bother me at all.
Pay attention to your hand/wrist/arm position while knitting & try not to have your wrist bent at too much of an angle.
If your wrists are bothering you, sleep in a brace. If you don't have a brace, you can ace bandage a ruler (or anything stiff & sturdy) to your wrist. Use whatever you have handy that will prevent your wrist from bending. Ridiculous, I know but I've done it before when traveling without my brace. Works like a charm!
Hope these ideas help,