Joyfully
Try going to your local library. I borrowed a book that was excellent on explaining proper posture and placement of hands, etc. so as to not tire or cause pain. One suggestion I remember is to use circular needles when doing a larger, heavier project. That way the bulk of your work will be sitting in your lap, not on one needle and the weight of it causing extra stress on your hands and wrists. Posture, if incorrect can also contribute to discomfort.
I am not able to remember the title, but I do remember it was a rather old edition with a plain, well-worn, brown cover and kind of thick, maybe 2 1/2".