Keep paint off of the trim
Paint rollers throw off a mist of paint that speckles everything below. Here’s the quickest way to protect doors and windows: Tape around door and window trim using tape that’s wide enough to project at least 1/2 in. from the trim. That way, you can stick light plastic to the protruding tape—there’s no need to tape the perimeter of the plastic separately. For doors, slit the plastic with a utility knife so you can slip through.
What to do if you get paint on the trim?
If you happen to slop some paint on varnished wood, don’t worry. Home centers carry liquid paint remover products for just that situation. Let the paint dry and mask off the paint you don’t want to remove. Gently scrape off as much paint as you can with a putty knife. Then squirt a few drops of remover on an old toothbrush and scrub away the rest.