How do you sit at a desk all day without wrecking your back and neck?

Position matters less than movement, but both help. Get the screen top at roughly eye level, since looking down is what produces most neck complaints — a laptop on a stack of books plus an external keyboard fixes this cheaply. Feet flat, hips slightly above knees, forearms supported. Then the more important part: change position every half hour, because the best posture is the next one. Standing desks help only if you actually alternate; standing still all day creates its own problems. Two minutes of movement each half hour beats one long stretch session.