I was in the same situation. I was a bit more sociable in highschool but since moving to another town and starting college, I began to be a lot more solitary and less outgoing. I've started doing a CBT program and a good step in becoming less anxious and more comfortable in social situations is not to set the bar too high, setting yourself up for failure. Instead of going to a socializing event cold turkey, try and build up to that. Do different exposures everyday that will work to lessen your anxiety so it won't be too overwhelming when you do go to an event.
It depends on what your current anxiety is like, but start with things that are relatively easy like asking someone for the time or for directions or inquiring about a product at a store. If that's too easy, do something a bit harder such as initiating a conversation with someone you know or may not know. It's about habituating yourself step by step to social/awkward situations. It would probably be difficult to go to a party right away and expect to start socializing immediately. Most likely it would be too overwhelming and ultimately result in awkwardness and a negative experience that would discourage you from partaking in similar events in the future.
Try and build up to that by doing small simple things, and as they get easier, progress to things that would be more challenging. You should find you'll be more comfortable and less anxious as you continue to practice these things.
