Keep moving or die. Always move evasively Since you have to keep moving to avoid making yourself a target, you'd better not move predictably, either. Dodging randomly makes it harder to draw a bead on you, and hopping about makes it hard to get constant, easy splash damage from rockets and such. Keep moving, and keep dodging. Getting used to mouse look at first is rather awkward, but very quickly you'll find yourself getting used ot it.
Enable mouse look.
You won't regret it. Configuring your key mapping to your liking With mouse look your free hand should rest on the keyboard. Configure the keyboard commands to you liking so that all the keys you need are in easy reach of your keyboard hand. Important also is the ability to switch back and forth, between moving and looking forward, moving forward but looking obliquely, and back to moving and looking in the same direction. Particularly while retreating, being able to make a break for it, turn around and keep up suppressive fire while still running away from the battleground.