Ask them to meet up sometime. That is basically about as difficult as it gets. You don't have to ask them if they would like to be in a relationship with you, at the first opportunity you get.
Biggy, knockbacks happen. Just say ok and move on. The less you try, the less likely you are to succeed. This doesn't mean that you ask each one of her friends out, one after the other, until you get a yes though.
Find out how.