can be pretty hard to sand if it's tongue n groove or square panels with moulding but for this job i usually sand every part to roughten it up and then wipe it down with a meths rag and then coat in white shellac based paint (zinsser BIN) cos that sticks to anything (even the bits you miss with the sandpaper!) and provides a sound surface to paint on and it also takes knocks so your top colour wont come chipping off later.
gillian, November 2009
Sand the varnish down first - but no need to spend your life doing it...just provide a key for the new paint - then give it a coat of primer and all will be well.
