Prime a wall that is already painted when you are changing the color tone. Start with a white primer in most cases, or use a tinted primer if you are using a highly pigmented color. Most suppliers will suggest this when you purchase bright-colored paint. This will help you obtain an even paint coverage and make a huge difference in the final product. It will also help you reach a truer version of the original color you've chosen.
Looks Can Be Deceiving
Don't trust the final product will look like the small paint swatch card you saw in the store ... it won't! There are many factors that change between when you look at that tiny swatch and then see your room fully washed in the same color. Lighting, paint sheen, wall texture — all play tricks on the eye and can alter the original color dramatically. To ensure you like the paint color(s) you're thinking about, test the color on a sample board first. Buy a quart of the color in question (some suppliers even offer smaller sample jars) and paint them on a 3-foot x 3-foot square of scrap wood (make sure you prime it as you would the walls you'll be painting). Next, place the board in the room and look at it at different times of day as the lighting changes. This sample board — and not the tiny paint swatch card — will give you a much better idea of the true effect the color will have in the room.
You'd Better Swatch It!
Make a swatch board that includes all the colors and textures you like for the space. Try to use swatches sized proportionately to the amount in which each color will be in the room. Take pictures of furnishings you're considering, or use sample fabric swatches when available. Seeing the complete picture in small scale will help you make changes before the money is spent.
Often people forget to consider the ceiling when choosing wallcoverings and opt for a neutral white or off-white color to not close in the room. While it's true white will give a sense of space, that shouldn't always be your goal. Think of the ceiling as the fifth wall in your room, and use a proportionate amount of color and texture to make it part of the overall design instead of something that goes unnoticed. Remember, ceilings like color too.
Here Comes the Sun
Consider the effect natural light will have on your room colors. This step is perhaps the most important when planning a color scheme. The amount of sunlight that enters a room, and for what portion of the day it is there, is important to note as this light greatly changes how you see colors. In rooms that receive lots of sunlight, a cooler palette will help soften the glare and create a less harsh effect. In spaces with less natural light or northern exposures, the use of warmer colors will add warmth where the effect of sunlight is most needed. Artificial light sources will effect your color palette as much as natural light will. Try to use fixtures with dimmers whenever possible. Dimmers allow you to adjust the various light sources around the room based on the time of day and mood you want to set; thus you can always show your color palette in the perfect light.
Emphasize With Color
Many rooms have features you'll want to accent, like a fireplace or beautiful old door. You can make these items a focal point by either surrounding them with intense color and keeping the featured item in a neutral or contrasting tone (for example, a white fireplace against a bright royal blue wall), or by painting a door and its frame in a color and making the wall more subdued (doing so draws the eye into the doorway, thereby enhancing its features).
Start With the Basics
Study the color wheel and the fundamental concepts behind it. Once you understand the basic principles, the world of color will open up to you.
Keep in mind certain visual tricks when choosing a pattern for wallpaper. Smaller patterns create the appearance of greater space and hide defects in the wall surface. Larger patterns produce a powerful impact but also make a room seem smaller. Avoid using striped wallpaper as the symmetrical patterns will emphasize crooked ceilings and corners.
Have No Fear!
Finally, and most importantly ... have no fear! In the end, design is a personal, emotional and very subjective decision. Act on your instincts and don't be afraid to break the rules. How we perceive — and our preferences for — color and texture is tied directly to our brains. Those colors and textures that make you happy will be a trigger for joy every time you walk into a room.