My advice would be : 

1) Remember to just have fun!

2) Have everything prepared before the jam.

3) Quality over Quantity. A small but vividly fun level is better than 5 awfully large, boring ones.

4) Make the core game ready in around 10% of the jam's time. As they say, finishing a game is super hard compared to starting one.

5) Last but not least, for your first 4 or so jams, try to make something you know how to make, then on from that, make things you never made before.

Thats all I have for now :)