It is as simple as this. Tell the next girl you like that you like her as a potential girlfriend. What this does is places you in the very small group of people that the girl absolutely knows that she could have a relationship with, right now. Think about that. I don't care how pretty she is, this is a very small circle of people. She will think about this and come to the conclusion that a known quantity (you) is much better than something else that may never happen. Then treat her like you would want to be treated but don't be taken for granted, and watch the magic happen.