I agree with the above by dancer with one exception, start with a couple of slower songs;a slow foxtrot and/or waltz. This allows the 80% to get on the floor and
just sway to a waltz or box to a foxtrot. Now if its a dinner dance the first set whether its before dinner or during dinner should be all slow; people are just meeting and greeting and talking then. During dinner your mostly providing background. I mostly attend gala dinner dances and the crowd mix is as said above
maybe a bit worst say 85/15 . You DO pick up some of the 80% with the "Rock and Roll" . You have to watch the crowd and be flexible. Ive been to event where there are only two or three "ballroom" couples out of say 50 couples and this is within the last seven years when ballroom had an upswing. Oh and if you're doing this in the
carolinas/No. FA . People will want to carolina shag and 80% can.

I have seem many good jazz bands play miserable ballroom programs. Once it was so bad that the good dancers waited for the canned music during the breaks to take to the floor! Or the conductor that announced, "I don't know if you can dance to this but here it goes..."

IMHO, please, please, please...

Keep the tempo constant. Dancers don't like "creative" tempo changes.

Play with exact, correct tempos, although some dances tolerate range of tempo more than others. Waltz standard is 87 bpm. Foxtrot cannot be danced SLOW -- don't think you are doing older dancers favors by slowing down their Foxtrots. Realize that in EC swing, the "real" swing, triple-step, needs slower tempos that single-step. Pepping up your swings to fast tempos will frustrate the triple-steppers. Rumba has a range of tempos, but works best in the 100-110 bmp range. And so forth.

Be a but careful, though. Full, standard-speed Quickstep's and Viennese Waltz's demand good dancers to keep the floor safe! These you can slow a bit.