After opening i usually freeze and dont know what to say, and the conversation gets really awkward, what can i do to keep the conversation to keep going?

You need to put some forethought into what you want to say to a girl. We call it a routine. Have some stock topics of conversation to talk about already in mind. Ask her if she thinks guns should be made illegal in light of the Sandyhook school shooting. Ask her if she thinks Lady Gaga is a man. Have a backup if she has no opinion or comment on any of those topics. If she has nothing to say about those things, ask her "You aren't good at talking to people are you? Are you one of them Aspergers people or something?"

Then if she doesn't laugh or open up a little bit, move on. Sets like that aren't going to get you anywhere anyways.

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“Nothing is impossible, the word itself says 'I'm possible'!” ~Audrey Hepburn