Two things on this one. Volume and song selection - things you can tell your DJ ahead of time through email or whatever….With volume of the music, people start experiencing hearing loss at 90-95dB. I'm hoping that your DJ has a way to measure decibels, because you don't want to expose guest's ears to anything more than 90Db during the long span of the reception. As for song selections, you should be able to make requests to your DJ or even build your entire playlist. Something that's sure to make guests enjoy the music most is to throw in a wide variety of music - country, dance songs, remixes, classic rock, slow dance songs, and of course, the classic reception songs like "Shout" and "YMCA." And this one's up to you, but I might also avoid songs that are really promiscuous or full of profanity. With the wide variety of people at your wedding, possibly including older people and children, songs like that are uncomfortable. Do you really want your grandparents to see you shake your booty to "Blurred Lines?"