I have been skim coating walls and ceilings for many years. Skim is a term to mean a thin layer of plaster or Joint Compound over a large area. This will smooth out the surface and help it look new and fresh as well as correct any unwanted texture or unevenness. 

Here is a ceiling I did in Nashville where I scrapped off the light texture and applied a few layers of plaster over it and painted it with ceiling paint.