Many of the NH/AL gigs I play are 'concerts' rather than 'dances' ... for these, I always set up a playlist, which all or in part will have some 'theme' attached to it - songs of certain artists; songs of certain songwriters; songs relative to the season or holiday etc. ...
Of course when you've played a facility a few times, you realize there are some favorite songs they ALWAYS want to hear ... one place I play I can't leave without playing "Sweet Caroline" and "NY NY" ... another place I always have to play "Goody Goody" ...
Playing in a restaurant, I just go by my gut, plus requests ... there is one place I play a couple of times a year, where I will usually see the same people and I know what they are going to request, so I try to beat them to it ...