A watch should be worn snugly enough to stay in place on your wrist without sliding up and down, but not so tight that it causes discomfort, restricts blood flow, or leaves marks on your skin. The commonly recommended guideline is the "one-finger rule" or "two-finger rule," meaning you should be able to comfortably slip one or two fingers between the watch strap and your wrist. This ensures the watch is secure but allows for enough breathing space to avoid irritation or numbness. Different strap materials may require slight adjustments in tightness — metal bands often fit a bit tighter to avoid slipping, while leather or fabric straps might have a slightly looser fit due to their flexibility. Overall, the watch should feel like a natural extension of your wrist without causing pain or excessive movement.