Rule 5

The player that won the previous round must toss first.

This means the player who scored the most points on the previous round (not their total score). In case the last round was a tie the player who went first last round continues going first.

The better looking player tosses first on the first round or whoever wins the ensuing fist fight to determine who the prettiest player really is. Alternatively, and surprisingly less bloody, a coin toss may be used to determine who should toss first on the first round. Of course you still have to decide who tosses the coin...