1. Clean Baseboards Before PaintingNowhere is it more critical to clean the surface prior to painting than when it comes to baseboards. Remember, dirt and grime collect at the bottom of walls. Wipe down with TSP and water with a soft rag.
Especially be sure to clean the top of the baseboards, as dust naturally collects on horizontal surfaces.
2. Do Not Remove Baseboards FirstIt is tempting to dispense with all of the taping and masking and oh-so-careful painting, and just remove the baseboards so that you can paint them on a couple of sawhorses outside.
While this may work sometimes, in other cases you will end up damaging the wall. Remember, too, that you will have to nail them back on, damaging your new paint job.
3. Forget About Cutting InThe "cut in" painting technique (painting without masking off surfaces) is difficult enough on accessible door and window trim, but far more difficult on baseboards because of their location.
4. Mask Off Wall and FloorUse low-stick painter's tape to mask the lower edge of the wall, right above the baseboard.
Even though masking off the wall and floor is a pain, it will result in a faster and cleaner paint job. You'll be glad you did it. But still be careful with your paint, because excessive paint slop on the floor masking tape will make the tape difficult to remove.
5. Patch and FillBefore you paint the baseboards, be sure to patch and fill any holes (nine times out of ten there will be depressions where nails are).
6. Paint the Baseboard First or Wall?This point is debatable, but I recommend painting the baseboard first. My reasoning is that baseboards are typically white, which is easily coverable with the wall paint color. So, if you happen to slop white baseboard paint on the wall, you can paint over it.
Special Note: Why Even Mask?
Let's say you have white baseboards and walls that will later be painted a darker color such as gray. Why even both masking the baseboards in the first place? Why not just slap on baseboard paint, and let the white slop over onto the walls? As noted above, it will get covered up, right?
Yes, but we're just talking about accidental messes of the minor kind. When you have a long, continuous line of white slop along the top of a baseboard, it can be difficult to 100% cover that white with the wall paint: some may show through.
It's just good practice to mask as much as possible.