Every designer will have their preferred method for selecting a color scheme for a project.  Many times their strategy will depend on the project and existing logos/collateral.  Here are three solid methods for picking a great color scheme from scratch.

1. Color Wheel – This method involves using a color wheel and a fairly mathematical method for selecting colors.  There are a handful of rules for selecting colors (analogous, monochromatic, complementary, etc.) that can generate very successful color schemes.  The best rule choice will largely depend on the desired feel of the final product.  There are some great tools for building color schemes online, such as Color Scheme Designer 3.
2. Color Matching – This method is far less scientific and much more artistic.  To do color matching, the designer finds a picture that they are fond of and feels could work as a cohesive color palette.  Nature does a great job of providing stunning scenes (sunsets, flowers, etc.) that translate perfectly to a color scheme.
3. Artistic Sense – This method is entirely artistic and involves the designer starting with a white canvas and building on it from scratch.  The technique can be difficult because it is very “right brain” and involves imagination as well as knowledge of color relationships.

No matter what method it takes to get there, a great color scheme is the key to a successful design.