Do I need to catch up on anything before watching Dragon Ball Super?
Having watched every Dragon Ball Super episode as they came out, I would say that so long as you have watched at least Dragon Ball Z, you are good. Everything important in Dragon Ball is roughly glanced over or built upon in Dragon Ball Z; the same is true for Dragon Ball Super. Dragon Ball GT is officially not canon material thanks to Super, so it is completely unnecessary.

That being said, at least knowing everything that happened in Dragon Ball Z beyond the Frieza Arc is pretty important. There are numerous very important events that happened in the Android, Cell, and Buu arcs that are quite useful to understand what is going on in Super. The main story of Super is not based on those events though, because Super is about Gods. It will make it very confusing to understand a lot of what they talk about and do. It is not sufficiently explained. Many things can probably be inferred in some way, but I guarantee that almost everyone who is not caught up in Dragon Ball Z will either be confused or spending a lot of time on the wiki and YouTube watching clips, thanks to Super.