Well dude...start hanging out with people...
Do you mean people hang out but they don't invite you or that they don't hang out? Well then invite people to hang out somewhere. Call up some of these school friends and say hey I'm heading to ____ hang out with some friends if you want to come. Then go out with these people and show them a fun time. Be crazy. Do things that people would say no no no we can't do that (nothing illegal lol just fun). Here's something I did, you can skip it if you want but I want you to get the effect of how this works:
I remember when I was in high school I went out with a bunch of people to a mall that had a kids fun area. There was this train for kids so I said come on guys lets ride the train
wooo. Everyone thought I was kidding so I decided I was going to go through with it and either look like an ass or the cool guy. I walked there and everyone followed. By suggesting this I automatically became the guy to look at. Everyone followed to see whether I would do it and naturally I looked like the alpha. When we got there the ticket guy was smiling at my suggestion...I knew it was going to work then so I turned around and all of them were standing huddled in a group looking at me. I could see that some of them wanted to come with me so I grabbed the hottest girl there and said with a big smile you're coming with me. We sat right up front where they have controls so kids can pretend they're driving lol. As much of the group that could fit on the train immediately joined us. It worked. I know it did so I just decided to have fun after. Putting my hands in the air and shouting wooooo. The girl I grabbed loved it and she joined me when I did it . I was the fun awesome guy from that day. The story spread to school of course and yeah there were some amogs who tried to amog me because of it but they were easy to deal with because they were so predictable.Just remember that people love to hang out with the crazy guy who'll take them out of their comfort zone...in a good way. Make a name for yourself. Publicity is good publicity