It depends on what you’re interested in doing.
I’m not sure how old you are, but I definitely recommend joining a social sports league. I’ve met some good friends that way. Personally, I’m partial to bocce and skeeball–kickball was okay for one season, but I’m not the kind of person whose main interest is to get wasted on cheap beer every weekend. (That being said, if that’s your thing, then you will meet a lot of like-minded people–totally nothing wrong with it!)
I started dating someone that I met online only a month or two after moving to DC. While I don’t necessarily regret it, we eventually broke up, and all of his friends that had become my friends weren’t my friends anymore, and I had to start over. So I’d recommend solidifying a couple of main hangs first, just in case.
When I was looking to meet new people, I also tried Meetup. None of the groups were particularly up my alley, so I started my own. I met a couple of people through that who are now my close friends, so you might consider that too. I recently joined a women in their mid-20s female friends group there, and I enjoyed it the few times I went.
If you’re interested in a fun night out that isn’t all bros, I’d try H Street, Columbia Heights, and U Street. I think H Street is particularly fun, though it’s kind of a trek from where you are.
I’m happy to make more suggestions if you’re interested!