Once she studies your hair, its condition, its style, its cut, and your lifestyle (e. g., how much time you plan on spending on your hair each day), she will then make some recommendations for color and maybe even a more suitable style for you. Plan on being there for a few hours.
Once a basic color is determined, now comes the fun and creative part. She may suggest adding lighter highlights around your face and maybe even dispersed throughout your hair. Lighter color near your face can change your entire appearance without the permanent commitment of an all over change.