A typical workflow to follow for painting rooms in a home internally, beginning with preparation and masking through to cleanup.
If at all possible remove everything from the room or at least move everything to the centre of the room leaving enough room for you to access all of the ceiling and all wall areas. Next cover the entire floor using drop sheets then cover anything else that has not been removed from the room with more drop sheets. Carefully check all around the room including ceiling, walls, doors and frames, window frames and skirtings for any holes dents and loose or flaky paint. Remove all loose and flaky paint, wash down any dirty or greasy areas and sand areas where any holes or dents have been filled.
Proceed to fill all dents and holes using a suitable filler, usually a powder based plaster is best, and fill any cracks with a flexible acrylic sealant which is usually packaged in a cartridge designed to be used in a caulking gun. A handy tip is to wipe over any areas that have been filled with acrylic gap filler using a damp cloth to remove all unsightly highspots or ridges.
When all filling has dried sand all areas back then paint over the patched areas with an appropriate paint or undercoat. When these painted spots have dried again final sand all surfaces of walls and ceilings doors and frames, skirtings ready for painting.
If trim areas such as doors and frames skirtings and windows require undercoating this would be the next step.
Next paint the ceiling and cornice using a paint brush and roller on a pole or an airless spray gun. If using a brush and roller, first brush the cornice and cut in around any light fittings first prior to rolling. If using an airless paint sprayer mask off any light fittings and proceed to spray around the corners and fill in the entire ceiling area. Repeat for subsequent coats of paint.
Next job is to paint the walls and if using a different paint to that used on the ceilings proceed to cut in along the top of the wall just under the cornice with a paint brush and paint any internal corners using the brush as you move around the room. Finish cutting in to the top of any skirting if fitted using the brush and then proceed to cover the walls completely using a paint roller. Repeat for subsequent coats of paint.
Finally using a good quality cutting in paint brush proceed to paint door frames, windows and frames and skirting boards and then doors using a larger brush or paint the doors using a brush and roller as described in this post.
Remove any masking materials including the drop sheets then sweep or vacuum the floor prior to returning furniture.