[1] Be respectful. (Only touch that which is yours or for sale; don't cheat; be mature)
[2] Respect the terrain. (Chop trees completely; replant; don't kill all animals)
[3] Don't make ugly builds. (If you can't build anything more elaborate than a box, hire someone or build underground.)
[4] Pranks must be reversible and scarce. (In other words, the person being pranked should be able to undo your prank. And don't do it all the time; that's called harassment.)