If you find yourself worried about the wording of a particular text, or fretting over which earrings to wear, or generally wondering how you should behave towards a particular guy in a particular situation, take a big step back and realize two things:
1. If he is really into you, you will have to make significant mistakes to make him change his mind. While there are always ways to make him like you more, your baseline should be to simply continue doing what you are doing and making gradual improvements. By "significant mistakes" I mean things like revealing that you are actually addicted to coke or gaining 30 pounds.
2. If he isn't that into you, no single small change you make is really going to attract him. A new set of clothes or "hard to get" attitude will not make the difference. You will need to revolutionize yourself to really hook him, and it is impossible to do this overnight. Instead, admit that he is a lost cause, and spend the energy that you would have spent on him on improving your appearance and personality. Then, by the next time a guy of that caliber comes along, hopefully you will have improved enough to make him stick around.
I am not saying that little things don't matter - they do; collectively, they matter a lot. But no single one will make or break a guy's attraction to you, and improvements to each one take time to implement and become natural to you. You need to be patient. But if you continue to make a steady effort, there is no question that the quality of guys you attract will improve.