If by "Dance music" you mean quicksteps, waltzes etc then an DNJ says tempo is everything. Get the tempo correct and people can dance to almost anything.

If by "Dance music" you mean informal stuff, then a useful rule is to play stuff that was popular when they were aged 15-35. So for a 50th party then anything classy from the 40's to the 60's should do, like Glenn Miller, Brenda Lee, Alma Cogan and of course Elvis.

Also mix up the tempo, don't go mad with uptempo stuff because they'll tire easily.

So have a selection of ballads, slow waltzes and maybe beguine handy as well!

good luck