From DIYinfo.org
Although they are not at eye level and so are not the most noticeable parts of a room, paint skirting boards with as much care as you take over the rest of the decorating.
Skirting boards are usually painted with gloss paint to match any other painted woodwork in the room. If the walls are to be papered, paint the skirtings before you hang the paper so that you do not splash the paper. As you paint the skirtings apply about 25 - 50 mm (1"-2") of paint to the walls also, this will be help to give you a better finish line when you paper.
It isn't practicable to lift wall to wall carpets before painting a skirting board, so you must take extra care to avoid accidents. Protect the carpet with dust sheets and hold a piece of cardboard under the brush so that floor dirt won't stick to the paint.


