I have two techniques.
First one, I choose places I like. This prevents most of it. If I know I don't enjoy going to a place for whatever reason (people and/or music mostly), after I've tried it I just don't go back to it.
Second, I'll just invite every follower I don't know in the room. There will be some uninteresting dances, but some nice surprises will also come. I do it all the time, slow night or not. It takes a little practise at first. Now it's just routine.
I do dance at least half of the time with people I DO know though, it's nice go have some fun with friends !
If inviting everyone still doesn't work, I'll go have a walk or something, or go chat with some friends, and come to the dance floor back 10-15min after. Not better ? I call it a day. It's no use crying over spilt milk. There are lots of great things I can do at home. Read a book, watch a movie, listen to music, ...
Yesterday, first half of the night was great, second half they switch DJ and the new one played crap. So I just went in another room to dance cuban for a bit instead, which was fun (even though I don't like cuban as much), then when I came back to xbody room most people were sitting (and I'm talking about at least instructor level dancers, not people being shy). I asked the DJ to put other stuff on, but he was obviously playing music for himself, not for the audience. So I went to chat with friends, which was nice, and went home a little later.
Overall, it went fine. Why ? Because I didn't let external events affect me. I had no control whatsoever over what the DJ played, so if asking didn't work, I had done my part so I felt fine about myself and was unaffected.
I hope this helps
To sum it up, my general view is don't try to change what you can't change. Figure out your options, pick one, and go with it.
PS: I stated this DJ problem to the organizer in a non-whining/theatening/complaining way and he took it very well because it was constructive. He said he'd try and DJ himself next time (he's a fantastic DJ, superb track selection and very good ability to read the audience).