As with every painting project, the long-term satisfaction of your work depends mostly on the work you put in before you pick up a brush. Proper preparation is key. Start by vacuuming and dusting your room, to ensure no particles end up in the paint as it dries. Put a drop cloth down to protect your floors, which also keeps dust out of the air.
Wash your walls thoroughly with a large sponge. Also, sand down any rough spots and repair any imperfections in the wall. Rinse with water. When the wall is dry, apply a primer coat of paint. If these proper preparatory steps aren't taken, your paint job could fall victim to peeling, flaking or bubbling.