Paint is the cheapest, easiest renovation you can do: it makes everything fresh and new, it covers defects, and its something almost anyone can do to a reasonable level of quality.If you just read that last part and started shaking your head because your paint projects always turn out terriblypatchy, or with visible sheen or brush strokes, or a final color that doesnt seem to match what you chose in the store at allthe cause probably isnt your work ethic, or an evil spirit inhabiting your house. The problem probably lies in your prep work. If all youre doing before you start slapping paint on the walls is applying some painters tape and covering the furniture, the chances that the final paint job will look terrible are actually pretty high. Here are all the things you should take into account before you dip that brush.Consider temperature and humidityThe weather can affect the quality of your paint job. Extreme temperature or humidity can have an adverse impact on the drying time. At colder temperatures, paint can thicken, extending its drying time. At hotter temperatures, it can dry too quickly, affecting adhesion. High humidity that leaves moisture on the walls will also result in a sub-par paint job.Your home is probably climate controlled, so painting inside even during extreme weather is certainly possiblejust make sure the temperature is between 50 and 90 degrees and the humidity levels are between 40 and 60%.Prep the wallsIts usually a good idea to wash your walls before painting them to ensure there is no dust or dirt that could adversely affect adhesion. While youre at it, look for cracks, dents, peeling tape, or other defects and patch everything up (including crayon or grease stains that will probably show through your paint unless theyre scrubbed off). A small flaw that isnt noticeable now might become a glaring problem when a fresh coat of paint brings it to the forefront.Cleaning walls with a dry microfiber cloth followed by warm water and a sponge is usually sufficient, unless your walls are really dirty. If youre worried about it, add a small amount of dish washing liquid or trisodium phosphate (if your walls are greasy and very dirty)but avoid colored soaps that might leave a tint behind.Choose the right rollersOne big reason paint jobs look like crap? The nap on your roller cover. The nap of your roller describes the thickness of the fibers. Generally speaking, the smoother your wall surface is, the smaller the nap of your roller cover should be. Painting kitchen cabinets? Go with a 1/4-inch nap. Painting a brick wall? An inch or even a 1 1/4-inch nap is best. Smaller fibers pick up less paint, while thicker fibers hold more painta too-short nap can result in a patchy finish on rough surfaces, while a too-long nap can add unwanted texture to smooth surfaces. Most interior paint jobs will call for a nap between 3/8 inch (very smooth walls) and 3/4 inch (textured walls, like stucco).Apply a separate primer coatThese days you can buy paint and primer together, which is a terrific time saver. But if your walls arent in great shape, even after cleaning and patching, you will usually get a much better result with a separate primer coat. This step might not be 100% necessary on your walls, but taking the extra time to prime properly will guarantee the best possible outcome.Identify the paint's undertonesAlmost all paint has an undertone (its base color )and a masstone (its overall hue). The undertone can be subtle and difficult to suss out, which is why its so important to paint a few samples on the wall before you commit. The paints undertone will interact with everything else in the room in ways that arent always obvious in the store. You brought home a beige paint, for example, but it has a green undertone, and suddenly it looks all wrong on your walls because your wood floors have yellow undertones.You can ask about the paints undertone at the store where youre buying it. You can also use a color wheel to compare it to primary colors to get a sense of the undertones involved.Combine multiple buckets of paintIf youre painting a small room and using just one can of paint, youre good to go. If your project is larger and youll be using multiple cans of the same color, you should combine all your paint into a larger bucket and mix it upa process called boxing. This is a good idea because even if you bought your paint from the same store at the same time, there can be subtle variations between cans. Maybe the pigments dispersed incorrectly, or the mixing process was slightly off. Whatever the reason, even the tiniest variation between cans will be incredibly obvious when you switch to the new can. Boxing it eliminates the danger.Check out your window tintYour windows can throw a wrench into your paint colors. This is because many windows have a very subtle green tint due to the presence of iron oxide in the glass. This isnt noticeable in any way to the naked eye, as a rule, but it can cast a greenish tint on your paint thats just strong enough to make it look inexplicably wrong in the daylight. Putting samples on the wall to judge the color is a great ideabut make sure you paint those samples in a spot where the light from your windows will hit them. Samples that look perfect in a more shadowed area may suddenly look weird when light hits it through the window.Figure out the color temperature of your lightsAnother lighting issue is your light bulbs. All the bulbs youre using in your light fixtures have a color temperature, and that can affect how your paint looks. Generally speaking, bulbs with higher color temperatures will brighten darker paint and mute lighter colors and vice versa. This means that a paint color that looks terrific in daylight can suddenly look grim or faded at night when the lights come on. Its best to check your samples in all kinds of light to make sure youve chosen wiselyand change your bulbs to support your paint if necessary.You should also check the color rendering index (CRI) of your bulbs. This is a rating between 50 and 100 that indicates how accurate the color rendering of the bulb will be. A CRI of 90 to 100 will show your paint as accurately as possible, reducing the chances that it will look worse when the sun goes down.Load your roller upFinally, when actually painting, dont be shy with your roller. When initially loading paint onto a dry cover, take your time and work paint deep into the nap. This can take a few minutes, so dont rushyou want a nice, wet roller when you hit the wall. When painting, dont roll until the roller is exhaustedreload frequently and keep the nap damp. Exhausting your roller will just leave streaks and faint spots that may or may not get covered by a second coatand may or may not haunt you for years afterward.