Strain Out the Goobers
Even if you open your paint right after bringing it home from the paint store, you can still have small chunks or strands of hard paint in it. If those end up on the wall, you'll have to pick them out and reroll the area. So spend two minutes straining out the goobers.
Buy a paint strainer at a home center or paint store or use old pantyhose to strain the paint. Place the strainer over a 5-gallon bucket, then pour the paint through the strainer. The strainer catches any debris in the paint. If you really want to be dollar savvy, rinse out the strainer in the sink and reuse it.
Paint Window Sashes Faster
Most DIYers slop paint onto the glass when painting windows, then scrape it off with a razor. But if you're good with a paintbrush, you can cut in along the glass. You won't have to scrape, and better yet, you'll leave the paint seal intact between the wood and the glass.
Load your brush and lay off the paint on the sash, staying about 1/2 in. from the glass. As soon as the brush is about half unloaded, go back and cut in closely. Let the brush bristles just barely touch the glass so the paint seals the tiny gap between the wood and the glass. If paint does drip on the window, scrape it off with a razor after it dries.
Groove Textured Ceilings
It's almost impossible to paint right next to rough-textured ceilings (a process called 'cutting in') without getting paint on the ceiling. Taping off the ceiling doesn't work either. The solution? Knock off the texture at the edge with a putty knife. Hold the knife at a 45-degree angle to the wall and run the blade along the edge of the ceiling. The blade scrapes away the texture and leaves a small groove in the ceiling. Clean out the groove with a duster or a dry paintbrush.
Now when you cut in along the top of the wall, the paintbrush bristles will slide into the groove, giving you a crisp paint line without getting paint on the ceiling. And you'll never notice the thin line of missing texture.