I tend to spend a little while customizing things at the start, and then stick with it. First thing I do with every new FPS is invert the aim, find a comfortable sensitivity, and if it's on the PC, set up the communication controls so it's something I can actually use (e.g., V for push to talk, T for general text chat, Y for team text chat...). Beyond that, it depends on whether I need to make the change or not; some really early mouselook FPSs default to arrow keys for movement, which means I have to spend quite a while setting them up. Other games I pretty much leave default; it varies.
Edit: Oh, also, for console games which have multiple presets for controls, I tend to go through them and find one I like. For example, on Halo Reach I always use the setting that was the default on the old Halo games, whatever it's called.
Edit: Oh, also, for console games which have multiple presets for controls, I tend to go through them and find one I like. For example, on Halo Reach I always use the setting that was the default on the old Halo games, whatever it's called.