Is your ideal girl actually one of your friends. It's a much more common situation than you'd think. First thing you need to understand is that you haven't hooked up or started a romantic relationship together for a reason. If you were compelling you would've been more than just a friend to her. It's as simple as that. So the first step is to accept that you need to be more and that because she now has a clear idea of who you are (the longer you've been friends the clearer) it's going to be harder to turn it romantic than if you were just meeting her. You are going to have to pull out all the stops to make her realize she has to re-evaluate you as a person. Imagine what you would have to do to attract the hottest girl in a club - that's what you need to - not because she's the hottest girl (potentially) but because you need to shock her into seeing you as the new you. The upside is that you have good logistical control. You don't have to worry so much about her flaking on you etc. because of your friendship. You are automatically going to see her, so you have many opportunities to steadily build up your new impression. It may take a while, but you have time. The two most important rules to start with are:
1) You don't do anything until she is giving signs that she is interested in you. Your job is to get her interested first, before you make any move on her.
2) NOT to hit on her verbally - this will be too alarming and unsubtle for her given your 'current friendship'. The example of the male friend confessing his interest in a girl (often seen in films) is the absolutely worst thing you could do.