Before you decide on the exact color you need to define the type of look you ultimately want to create and the mood you want to set.
Sometimes this is easy. For instance if you're painting your daughter's room and she insist on pink and you insist on her being able to sleep you are well on your way to finding your perfect paint color because you know the color family (pink) and have defined the mood (restful, tranquil, dreamy) you want to create. Jump on the fast track and go right to Step 3!
If however you aren't sure what color you want then start by thinking about the mood or feeling you want to create in the room. Is it a family room that you want to feel warm and welcoming? Is it a kitchen that wakes you up in the morning and energizes you for preparing a meal at the end of long day?
For every room you decorate you are setting the stage for the activities and interactions that make up your life. So if you don't already have a vision of the finished room close your eyes and see yourself or your family in the room, imagine how you want it to feel and and capture that with the colors you select.