if you're not a person who's very comfortable making conversation with other people you don't know so well, i just read a book that, though a bit hokey and cheesy, did have some useful pointers. it's by a woman named leil lowndes and though a bit unrealistic at times, has some great tips in there that anyone can use - it's called
how to have a conversation with anyone.
and take heart in the fact that your sisters see something in you that makes them think you'll be an asset to them during rush, even if you don't see it yourself
