Check out these good and bad practices when using paint color samples and testing different paint colors.
Paint color samples are great when you need to figure out the best colors to paint a room... but only if you use them properly. Here are some guidelines you may find useful when sampling and selecting colors:

rush the color selection process. Follow the steps - from finding painting ideas and inspiration, to making paint color swatches.
try to save a few dollars by skipping the sampling step. You'll end up spending much more if you make a paint color mistake and have to re-paint.
paint sample colors directly on the walls. First, your perception will be clouded by the current wall color. Second, the test areas may remain visible even after the walls are painted and mess up your new finish.
scatter paint color swatches all over the room. Make sure you view each one under the same conditions.
limit yourself to sampling only one color. You'll be happier with the end results if you try out 3 to 5 different hues.

stay consistent with paint sheen levels. If your topcoat will be satin, buy color samples with a satin sheen.
take some time to make oversized paint color swatches. That's the only way to see how the color will "read" in your home.
allow the freshly painted swatches to cure for 24 hours. The colors may deepen during that time.
check how the colors coordinate with your home design. Hold the sample boards next to window treatments, furniture, accent pieces, floors, ceiling, woodwork, etc.
use tunnel vision when evaluating paint color swatches. Avoid comparing them to your existing wall color.
live with the paint color swatches for at least 2 days. The colors will look different in the morning, in daytime and in the evening under artificial light.
consider when you use the room the most. Choose the color that looks good at that time of the day.
trust yourself. If the color works for you, it works. Period.
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See also:
Why NOT to Paint Sample Colors on the Walls
2 Unusual Ways of Using Interior Paint Color Samples
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