Get a (friendly) dog
An easy solution when searching for how to make friends as an adult is to get a dog. It’s amazing how many people you can meet by simply walking a dog. Dogs create—and require—routine. You’ll be out there at the same time, every day, and so will every other dog walker in your neighborhood.
Friendly dogs love the company of other dogs, so while your waggy-tailed friend is making a new buddy, you can be doing the same thing. Also, seek out the dog parks and runs in your area, so you have more opportunities to meet other people and to establish relationships with them.