As I have just finished my 3rd Jam, I thought'd I'd like to discuss what GM48 is to me.
GM48 isn't about the winning, it's not about the place you get. It's a learning experience. You can be completely new to GM, or have years of experience. Either way this jam will really help you. There is always something to be learned in Game maker, from simple things like bug fixing, to harder like organisation and time management.
Whatever you do, don't get put down by the other developers better than you, or by your rating, low or high. Focus on what you've achieved, and what you've taken for the jam. Read through the feedback and be open to suggestions, take them as notes for next time.
However good you are at game maker, GM48 will help you learn more.