getting fraternity bids

How do fraternities give bids? I know it helps if you are old friends with a brother or go to parties and know most of the chapter but what do they do with kids they meet during rush? There is no way I will meet people from every fraternity and it's a struggle to expand my connection and friend base. Do fraternities, especially "higher" ones, give bids to kids they meet during rush? Any suggestions on how to meet more greeks? Right now I'm relying on chance and its working ok but I want to meet more people without seeming desperate. And instead of telling me I won't get a bid because I'm on Greekrank just help me.