Map choice
The terrain has to be one randomly generated by the in-game editor, try
to select terrains that minimize the number of easy kills and big piles
during the first turns of the round.
Play fair
Respect the first-turn-order, don't choose terrains trying to maximize
the positive effect of you starting a round or to reduce the positive
effect of the other wormer starting a round. Don't quit the game after
each round, because besides being annoying it is suspicious. Also you
shouldn't change your team, worms name, worms order and/or special
weapon between rounds, it is very lame.
Forbidden bugs (Remember that rope/bungee knocking is allowed)
* Bungee from Jet Pack (unless both players clearly agreed on allowing
this).
* Bow/bat/rope angle modifications.
* Walking on top of the indestructible barrier of a cave.
* Skip walking using the mouse.
* Floating weapon glitch
* Jumping from Pneumatic Drill
* Jumping after teleporting (turning around after teleporting is allowed
because it doesn't change the worm position).