Painting walls with latex paint is one of the most common do-it-yourself projects, but home owners often make mistakes that look bad or even force them to paint all over again. Some of those mistakes ­occur before the DIYers even apply paint—when they buy equipment and prep the walls. Here are 12 tips from an experienced painter that will give you prolike results when you paint your walls…

Selecting Supplies

Home owners often spend hours picking out the perfect paint color…then just grab any nearby rollers, brushes and other supplies at the home center. That’s a mistake. Using the wrong tools makes painting harder and makes the result worse, too. The painting supplies you should buy…

Brand-name ⅜-inch-nap, nine-inch-long roller covers. Home centers and painting stores offer a wide range of roller-cover options, but a nine-inch length with a ⅜-inch nap (the depth of the roller’s pile) is almost always a home owner’s best choice. A nine-inch length is large enough that you can paint quickly but small enough to be manageable. A ⅜-inch nap holds lots of paint yet still produces a smooth finish.

Exceptions: A slightly shorter nap could be appropriate if you want a very smooth finish and are willing to take more time (it holds less paint)…a slightly longer nap could be appropriate if you are painting a rough surface such as concrete block and don’t mind that textured finish.

Brand-name roller covers are worth their higher price—they hold paint better than off-brand covers and are less likely to shed lint into painted surfaces, which looks terrible. Good roller-cover choices include Purdy White Dove and Sherwin-Williams’s Contractor Series Soft Woven.

Also buy a roller handle (what pros call a “frame”) with an extension pole long enough that you can use the roller on your walls and/or ceilings while standing on the floor, not on a ladder. This will cut painting time in half.

Paintbrush with Chinex bristles. Chinex is a DuPont nylon that holds its shape and stiffness very well and cleans up easily. A two-to-three-inch-wide Chinex-bristled brush might cost $15 to $20—they’re not cheap—but it will last a long time if you prevent paint from drying on it. To do this, clean the brush with warm water every two to three hours even if you intend to go right back to painting. Recommended: Corona Performance-series Chinex-bristle brush. An angle-cut brush is a good choice for painting walls near trim or ceilings.

Canvas drop cloth. DIY painters tend to put little thought into drop cloths—many just use old sheets or shower curtains. Only later do they learn that paint can soak right through bedsheets and can roll right off the ­edges of plastic shower curtains. It’s worth buying a thick canvas drop cloth—a nine-foot-by-12-foot one can cost as little as $20. Or pay a bit more for a canvas drop cloth that has a slip-­resistant coating on one side to reduce the risk that the cloth will slide when someone walks on it, causing a fall or shifting a ladder.

Deep-well roller tray…or a paint bucket and grid. The deeper your paint tray, the less time you must spend refilling it. Buy disposable paint tray liners, too—they save you from having to clean your tray. Or do what many pros do, and skip the tray entirely. Instead, dip your roller directly into a bucket of paint. To do this, buy a five-gallon bucket large enough to fit a roller, and buy a “paint roller grid.” Hang this grid inside the bucket, and roll your roller along the grid to remove excess paint as you would on the incline section of a paint tray.

Prepping to Paint

Use a degreaser before painting surfaces within five feet or so of a cooktop. Paint will not stick properly to kitchen walls, ceilings or cabinets if these are coated with the oil that typically comes from cooking. Use a product specifically designed to prepare greasy surfaces for paint. Do this even if the surface to be painted is not visibly greasy—applying a degreaser once is a lot easier than painting twice. Example: Krud Kutter Prepaint Cleaner, typically $10 or less for a 32-ounce spray bottle.

Press down on your painter’s tape…and then press again. When DIYers peel away painter’s tape after painting, they may discover that paint has gotten underneath. The fix: After you position tape, run the pad of a finger firmly along its length to improve the seal. If the paint job takes more than an hour or so, run your finger along the tape in that section once again.

Combine cans of store-mixed paint if you expect to use more than one. If you are going to use multiple cans of the same color paint, mix them all together in a five-gallon bucket before painting. Pros call this “boxing” the paint. Paint stores don’t always mix paint exactly the same for each can, so if you don’t do this, some sections could end up being a slightly different color from others.

Add latex extender to latex paint before applying it with a brush. When DIYers brush on latex paint, their brushstrokes often remain visible. Pros use an additive that causes latex paint to dry more slowly and smoothly. (This additive isn’t necessary when latex paint is applied with a roller.) Recommended: X-I-M Latex X-tender, less than $10 per quart—enough to treat five to 16 gallons of paint.

Tips for Applying Paint

Paint edges first. Use a brush to “cut in” paint on the wall around moldings, ceilings and other edges before you use your roller on the rest of the wall. DIYers sometimes do this in the reverse order because they want to delay doing the tricky edge bits as long as possible—but doing the edges last often results in a visible “halo” effect around fixtures, windows, doors and other edges because the brushed area overlaps the rollered area rather than getting hidden beneath it.

Load up your roller with lots of paint. Painting with too little paint on a roller, known as “dry napping,” results in tiny gaps in the paint. A too-dry roller even could pick up paint already applied, rather than lay more paint down.

Not sure whether you have enough paint on the roller? Listen. A dry roller makes a hissing sound as it rolls along the surface. A roller with sufficient paint sounds moist. (Once you hear these sounds, the difference should be clear.)

Tip: Some DIYers use too little paint on their rollers because they want to avoid the drips that can occur when a roller heavily loaded with paint is lifted to the wall or ceiling. These drips can be minimized by rotating the handle of the roller 180 degrees once or twice to reverse the drippy paint as you lift it.

Load up a section of wall with paint, then even out that paint. Don’t try to make paint look perfectly even from the moment you apply it to a ­surface. Instead, first get enough paint onto every part of a section of wall roughly two to three feet wide. Apply enough pressure to the roller to get the paint down into the texture of the surface, use enough paint so that there are no tiny gaps, and overlap your previously painted section by around half of your roller’s width. Then position your roller at the top of the section, and gently and smoothly roll from top to bottom in successive swaths, taking the roller off the wall each time you reach the bottom, to even out the previously applied paint in the section.

How to Paint Trim

If you are painting both walls and trim, paint the trim first. Apply multiple coats of paint to trim, if necessary, and wait for these to dry completely before taping off trim and painting walls. (If you’re painting the ceiling, too, paint it after the trim but before the walls.)

Use an airless sprayer—a sprayer can’t leave brushstrokes. Such sprayers can be rented at many home centers and paint stores. Be sure to follow the directions that come with the sprayer and to carefully cover surrounding areas with tape and plastic sheeting.

If you don’t want to bother with a sprayer, use a brush that’s made for trim and that has 100% polyester bristles such as the Purdy XL Glide angle sash brush. The soft bristles make such a brush less likely than others to leave brushstrokes. And use a latex ­extender, such as the X-I-M Latex X-tender ­described in the main article, when applying latex paint to trim—without this, latex paint is more likely to dry too quickly and leave brush marks.

As with walls, the best strategy for painting trim is to first get sufficient paint onto every part of the trim…and then “lay out” that paint using long, smooth, single-direction strokes.