Is this for your wedding? If not, seek close bride and groom input!
We got married in April, and I did all the music and “DJ’d” (left a playlist running for the most part). A few ideas (that, in true STW fashion, don’t answer your question):
Put out a call for songs from wedding guests – we had a suggestion box on our RSVPs, and also a link to a collaborative spotify playlist that people could add songs to.
Set a playlist up in advance, but be prepared to accomodate requests/alter things according to mood on the night.
If you’re DIYing, make sure you have a reliable PA on the night and have tested it in the room beforehand to make sure it sounds OK.
Have fun, it was one of the things I enjoyed most about our wedding reception, both in terms of putting it together and running it on the night.