Best thing to do? Rip them off and fit new ones!
No, I'm not kidding. This is by far the easiest way to deal with them, you get a better result and you'll never have to touch them again.
Buy skirting the same thickness as the stuff that's on, or thicker, or you'll get a gap to the carpet. Try to pick the wood yourself or they'll give you junk.
Stain all the wood before you cut it down or fit it, much easier. Two coats of stain/varnish on the front, with a light sand between coats, and a coat on the back to stop the crap wood warping.
Take care when removing the old stuff in case it's stuck to the wall paper etc, run a knife down the back of it. Buy a mitre to get the joints right. Cutting it down and fitting the new stuff it is very easy and you'll have shiny new skirting boards that you'll never need to paint again :0)
The only tricky part is the door checks, the flat part on the inside of the door frame. It depends what they are made of. If they are made of wood or plywood you can just turn them over! Prise them off, with big flat blades like chisels for instance, sand the paint off the edges, stain the reverse and refit them nice new stain-side up.
