I would not recommend going with a smaller TV as I find the crisper and clearer (which comes with bigger TVs) the image, the easier it is...
But yeah like I said, start with a very low sensitivity and work up from there.
I have it set so I really have to crank on the sticks to swing around fast, this helps keep my aiming smaller and keeps me from just going wild.
Also, use bursts. Never just hold the button down and spray.
One more thing you gotta realize is how much you move when you get hit, this messes with your aim a lot, so avoid rushing into groups and firing. You won't get kills that way.