If you live in a big city? you have many options, such as volunteering for most anything.
Or join a "meetup" online, of your favorite hobby or interest.
If you are looking to go out with and meet people of the opposite sex then go out to live rock bands, the hot dance clubs or learn some social dancing, "swing, rockabilly,country or whatever".
If you live in a small town, then visit the next towns that have things that are going on? "bowling terminates, church activities, gun clubs, cattle tipping, making crop circles, HAHA HEHE. just kidding but go out and do somthing. As niki shoes says, JUST DO IT...