Have fun. Remember to sleep and eat and stuff.
As they've already mentioned: keep the scope small. In my first jam, we (team of three) did a game with five levels. Bad idea: the pixel art alone was forty hours of work.
It helps if you have the game engine and any other software you need already downloaded and ready to go on your computer before the jam starts. (I did not do this in Mini-Jam 61...). Having an idea of roughly what kind of game you want to make can help, too: 3D or 2D? Top down? Platformer? FPS?
Welcome to the party :D