1. Reconnect with OLD friends first. If you have a bunch of friends on Facebook that you never get together with, that's a good place to start. Once you hang out, you might start meeting people through them.
2. Don't TRY to be interesting. Meaning try not to worry about whether people like you. Just ask a lot of questions and be interested in THEM. It takes the pressure off, so you can be yourself. And it makes it easier for the two of you to click.
3. Be willing to open up to them a little. Meaning talk about real stuff, don't just make small talk. You don't want to open up TOO much too soon. But you won't be close friends with someone if you only talk about the weather.
4. Touch base, at least every two weeks. A study in 2008 found that lifelong friends tend to talk at least once every 15 days. Even just a text is fine. If you don't have a ton of friends, maybe you didn't try hard enough to stay in touch with OLD friends.
5. Join a group. It's a lot easier to make friends with people if you have something in common. Denmark is supposedly the happiest country on Earth. And it's partly because 92% of the people there are in some sort of group where they can socialize.