Preparation work is the most important part of painting a wall. If the preparation work is poorly done it will show through the paint and just make the wall look awful. The first thing you need to do is remove all furniture in the room and lay down a drop cloth. If you cant remove the heavy furniture you can lay a drop cloth right over it to protect it from any paint that may get onto it during the painting process. I recommend using a drop cloth made of a canvas material rather than the cheap plastic ones. The canvas material lays better on the floor and wont move or rip like the cheap plastic drop cloths will. Next remove cover plates from switches and outlets, taping the screws to the back of the plates is a great way to assure you don’t lose any screws. Once that is completed your going to want to scrape away any lose paint. Once the loose paint is removed it is now time to patch any small holes or nicks you may have in the wall using Spackle. Apply a spackling product with a putty knife and smooth it out, once the spackle is dry and done to your satisfaction grab some sandpaper and smooth it out. Remember the higher the grit the sandpaper is the smoother the area will be. Once that is complete your going to want to vacuum up any dust that has gotten on the baseboards or molding. Next wipe the walls down with a damp rag, a quick once-over will do the job this helps to removing any remaining dust that might be on the walls. The final step is to tape off anything you don’t want to paint such as the baseboard or the ceiling with painter tape. After the taping is done the wall is ready to paint.