1) Do not monopolise the group
Do not be the only one that talks. Group work only gets done when everyone works together.
2) Do not be quick to judge
Do not be quick to judge someone else's ideas. A "underdog" may have the best idea!
3) Have fun! (but not too much)
It is always better and more productive when everyone has fun, but it may start having negative effects if everyone starts having too much fun.