What was it specifically that you liked about it? That could help with others making recommendations.
If you liked the element of people in a confined area, jockeying for power and using their personalities to change events...then you might like Hitchcock's Lifeboat.
If you liked 12 Angry Men, I would also recommend the TV remake with Jack Lemmon and George C. Scott...just as good as the original. I would also recommend the 1959 film Anatomy of a Murder and 1982's The Verdict.
When I watched 12 Angry Men, other members recommended to me Witness for the Prosecution and Judgement at Nuremberg. Those were excellent recommendations and now I pass them on to you
And then the last of the original trilogy 14 Hell-bound Men
After you're done with the original trilogy, you can dive right into the rest of the 12 Angry Men shared universe in any order. My favorites are 44 Drunk Men, 341 Men dressed as crows and 666 's.
Yeah in all seriousness, I'll recommend for you to watch as many movies on the AFI lists as you can.