what songs, decorations, and games should i have for my 14th birthday dance party?!

Me and my best friend are having our 14th birthday partys together. Its going to be at a party room in our rec center. We are gonna invited around 80 people. we have already hired a d.j. but we need to come up with aboput 50 songs for him to play. any ideas? we also need a theme. and decorations. we would appreciate any ideas you have!