I'm sure this is different from chapter to chapter, but between bid tuesday and our AM program (pledge period) we gave a list of our top ten picks for a big brother. Then the Fraternity Ed. guy goes through the list, crosses out those that aren't eligible or don't want to be a big bro (which is almost never). If more than one person has a guy first, he chooses which one he wants. Then, they just go down the list.
If I were you, I wouldn't worry about it until the time comes. Unless you get in a house of utter @$$holes, you will get a big brother that you like and have something in common with. Things work better that way.
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Steve Corbin
Lambda Chi Alpha
Theta Kappa Chapter
Rose-Hulman Inst. of Tech.