Protect the floors, furniture, your clothing and yourself. Place drop cloths over the floors and any furniture or appliances that cannot be moved. Be sure anything that you don't want to have paint on it is covered. This includes yourself. Wear protective clothes or overalls or old clothes. Plastic gloves can keep paint from covering your hands and protective eye wear is also important, especially when painting the ceiling. A respirator is also importan to keep from inhaling paint droplets.
Prepare the paint. Most paint must be diluted to work in a sprayer. Be sure to follow the instructions provided with your sprayer to ensure paint is the right consistency. Fill the sprayer according to instructions. If your sprayer is rented, be particularly careful to follow instructions, as you will be liable for any damages.
Start with the ceiling. Mask the tops of the walls with painter's tape and brown paper or plastic if the ceiling is to be painted a different color. Spray an even coat over the surface, being sure not to create too much overlap between each strip. Several light coats provide a better texture and better coverage than one heavy coat.
Prepare the walls. Mask the ceiling edges, as well as all trim such as floorboards and window frames. Remove outlet and light switch covers.
Paint the walls just as you did the ceiling. Paint in slow, steady strokes for even application.