Test paint your chosen colour(s) on a piece of cardboard and move it around the room. Then you can see how the colour is perceived in different lights.
Measure the surfaces to be painted so the paint shop can work out how much paint you need.
Move out as much furniture as possible to make room. Sofas and heavy furniture can be covered with furniture plastic if they are difficult to move.
Remove wall sockets and switches so you don't have to mask them. But remember to cut the power first!
Leave screws in any screw holes you may want to leave after painting.