Hello. I was in the gmtk game jam and was not able to publish a game, but I have a couple things that I learned from it. The first thing is to have a working product in 24 hours. This is really essential because the last 12 hours of a game jam should be spent polishing. The second thing is to create a list of things that need to be done, and to make sure that they get done. The third is to exercise a lot before and during the game jam.
I happen to have a lot of time on my hands in a week, but getting down to the game's core first and spending as little time as possible on it is wise indeed. Also, I'm already practicing like never before. If only you knew the many many many many problems I would have met if I didn't practice first (like technical difficulties with music production, for example). A disaster has been avoided.
Great advice overall! Thanks a lot! :D