Now let's look at your question again, you say that ".. i like some really pretty girl," in what way is she pretty, looks great? If that is the reason, you basically have your answer. If you yourself have rejected all the uglier ones for this pretty girl, can you expect her to reject all the prettier boys for you. Seems like simple logic to me.
But as they say, beauty lies in the eyes of the beholder. As all the previous posts have put it, try to be a nice person, someone that people would be attracted to for his inherent qualities.