Only Make As Much Sound As You Need To
If you walk while crouching you are virtually noiseless. If you are in an area, usually a town, and you don't know anything about it (i.e. there could be a bad guy anywhere around you) the game becomes submarine combat and the noise you make are the pings.
The less noise you make and the more noise your opponent makes the better the chance you'll be able to ambush them.
This is goes in tandem with point 2, about not being prone. If you are prone and moving about everyone nearby knows where you are. If you are forced to go prone, keep your butt still.