Self-explanatory. Don't blow someone's thing up, don't cover it in lava, don't destroy it.
2. Pranks are allowed
Feel free to prank people.
Allowed: Fill their house with beds, Place a noisy redstone contraption nearby.
Disallowed: Destroying part of their base. Destroying their items. Irreversible damage.
3. No Stealing
Again, self-explanatory. Don't take peoples items. Don't kill people for their items.
4. No Hacking
No xraying, fly hacking, or using any clients which give you a significant advantage.