When/How to approach a woman?

OK, so asking the ladies, b/c yar the experts, b/c hey, I'm asking about women. *l* This is going to be a multifaceted question. So, say I'm out and about and see a woman I'm attracted towards and want to make a play, but not certain where she's at with me. How can I tell if she's interested? Is there a body language to look for? or do I just go up and introduce myself? See, the fear is that I'll go up and she'll tell me to take off or even laugh at me (yes, fear of rejection). So, I'm wondering if there is some way to tell if she's interested in me as well or once again, do I just go up and chat with her and overcome my fears?