I adore Game Jams, Absolutely LOVE them! But there are skills you have to attain before you join. First, Scoping. You make a game too big? You either don't deliver or you deliver an experience you wont be proud of. You'll learn plenty about your discipline and scoping in the process, and you might even learn a more important skill (Not hanging on the outcome, but loving the process instead). Second, People Reading. Can you pick people out that you think will deliver? Will stick to brief and not go off on their own to do whatever they want, aiding in the delivery of a disjointed, messy, bare project? Or, can you spot the people who will deliver something that they can be proud of as well as you? So, the skills to develop are, people skills and scoping.