Use Raw Input
Many games have an option to turn raw mouse ipnut on or off. Mouse movements are typically much more accurate using raw mouse input, especially in first person shooters. It varies game to game, but in some games with raw mouse input off the mouse aiming will be very inconsistent, especially with higher DPI settings. The raw setting takes mouse input directly from the mouse instead of from the operating system which will change the input based on things like cursor position on the desktop which can limit the maximum turning speed and create inconsistent turning speed.