Ask a roomate of yours to be a wingman for you. Go to your nearest bar and generally just try to loosen up a bit! I think a lot of people feel weird talking to new people after coming out of a relationship - it's natural, seeing as you were so used to having your attention on one girl. Girls love to talk, so don't worry about not having a reason to talk to them. It's literally in a girl's DNA to talk and connect with people.