A paint-by-numbers kit comes with a numbered canvas and corresponding pots of paint; find a numbered section that matches your current paint color, and fill in the entire area. Be cautious not to paint outside the lines, and let each color dry before moving on to the next one.
Painting by numbers is a great way to learn how to create complex images through different shades of paint, and it's also a relaxing activity for those seeking a casual yet creative outlet. A useful strategy is painting color-by-color rather than section-by-section. Using the darkest color first, paint all the sections that match that paint's number, going from the largest areas to the smallest. Control the brush carefully to keep the paint within the lines. Wash the brush thoroughly with water or solvent before using a new color of paint.
Some paintings require you to mix paint, usually indicated by two numbers in a single area. Because these sections are the most complex, you should fill them in last. Using the paintbrush, drip equal amounts of the two colors on a washable, solid plate, and gently mix them together with the tip of the brush. Then fill in the area as if it were any other section.