If you're painting via the DYI method to save some money, you may be scratching your head, wondering what to paint first: the wainscoting, the walls, the trim, the baseboards, or the woodwork. You're not alone. Even experienced painters are divided on this subject.
On the one hand, if you paint the woodwork first, any spatters and drips that end up on the walls will only need a bit of feathering out rather than actual removal. That's because you're going to paint that wall anyway. Also, many people feel that getting the nit-picky, fiddly painting out of the way is a big relief and makes the rest of the job of covering those big flat walls easy as pie and a big relief.
On the other hand, most people paint walls with rollers. Rollers tend to spray bits of paint into the room as you cover the walls. No matter how careful you are, some of this spay will end up on your woodwork. So it's a tradeoff and what you decide to paint first all comes down to personal preference.
One thing is for certain, when you do decide to paint the woodwork, whether you do this first or last, look it over for imperfections and make any repairs prior to painting. If the woodwork has had a past finish of glossy paint, make sure to sand it first to get better adhesion. If you prefer, use a liquid deglosser.
If you're sticking with one finish in one color for every surface, you may want to just paint trim as you get to it while painting the walls. This is something that is possible if you keep in mind that you will need to alternate between the sash brush and the roller. This should work out for a room with only a single door and not more than two windows. If, however, you decide on painting the trim first, it's a good idea to let it dry, and then tape it off with painter's tape before you paint the rest of the room.
The technique for painting the top of the baseboard is to paint using downward strokes. Use 5-6 short strokes and then go over them with one long smooth stroke. Next, take a thin segment of cardboard, or a painting shield to use as a portable masker and cut in the area where the baseboard meets the floor. Paint only 2-3 feet of the baseboard at one time. Watch for spatters, drips, and overlapping edges and make sure you clean these up right away. If you wait until the whole baseboard is painted, these flub-ups will have already begun to set.