There are several reasons and meanings behind star tattoos. You could look at them in terms of hopes to being a star or your goals and determination to reach for the stars and be all you can be (no pun intended). Otherwise, for the most part the meaning behind a star will depend on the type of star.
Star tattoos can be as simple as the choice to study in astronomy, or as complicated as to signify the birth a child.
Star tattoos can represent a significant change in one's life or a desire to achieve high goals. Maybe it represents a bright, shining point in your life.