All specific songs for dances, intros, etc., should DEFINITELY be picked out prior to the wedding. As far as the cocktail, dinner, and dancing music is concerned it really depends on the DJ. Some DJs want to have all their music ready to go prior to the event. I however, like to have a general idea of what the client wants, as well as the ages, ethnicity, dress, and amount of alcohol consumed by the guests. I like to have a general idea and then show up and read the crowd accordingly. I probably prepare for the client and guests personalities more than I do the music that I will play. But every DJ is different with this. After over 28 years of DJing weddings the spur of the moment selections are a bit easier for me than others.