The fact that you don't want to screw up will make you screw up at the end. The number one rule to getting your game up is by accepting the possibility of failure. If you don't want to screw up subconsciously you will always be thinking in your head when your with the girl "did I screw up or is it just she tired" "did I screw up or she's just busy and therefore not replying to my texts" etc.. get the point. On the other hand if you embrace failure you will not be thinking about yourself screwing up and instead will concentrate on your interaction with the girl. As far as how you should open that's up to you. Say anything "hi" "hey how's it going, haven't seen you in long time" the main thing is not to show to much interest from the start.