sand the walls. Get red flakes of paint all over you. Remember halfway through that you should be wearing a mask.
Step Two: put a gunstock gray primer over the mess that you just sanded. The whole time in your head going "take that you (^&* red paint!".
Step Three: Wake up next morning and see gray primer. And the mess you made out of your baseboards and trim with the red. Look at the splotches on the ceiling and your uneven paint line up there. Decide to buy trim to cover boo boos.
Step Four: Apply red paint...coming soon...