Section I: Griefing
Griefing is defined as destroying or changing someone else's blocks without their go-ahead. This also applies to any plot they've built on. Look at building rules for more info. If you grief, you'll be banned and rolled back. If you want to report a griefer, there's a forums section that you can do it in. A staff can replace or rollback anything that gets griefed, they do not have to rebuild though.
Section II: Stealing
Stealing is not allowed. If you steal from someone's chests, furnaces or any other container, you'll be banned. If someone's loot is on the ground, you are not allowed to take it, they're probably out to get it back. If someone steals from you and your stuff isn't locked, staff do not have to replace it.
Section III: Building
You cannot build within 5 blocks of anyone else's buildings unless a town's rules say so as this is considered a form of griefing. Giant 1x1 pillars are ugly and are considered by most people a form of griefing, these must be removed after being built. Lag generating structures are not allowed unless they can be turned off by a switch and are left off unless being used. Diamond blocks are highly griefable, so only use a minimal amount. Duping Machines are not allowed. This is item exploitation and will get you banned. Town rules overrule server rules if they are agreed upon by the people living there and the staff.
Section IV: Item Spawning
Giving out spawned items will get you demoted or even banned, do not do it. Only give them away for a joint project and only give the exact amount for the project.
Section VI: Shops
Shops are okay as long as they don't sell spawned items (refer to the rule above this).
Section VII: Banned Items
Fire Blocks and TNT are banned items. If you have any of these you may be banned.
Section VIII: Mods
All Clientside mods are banned except ClientSide Mini Maps, Optifine, Too-Many-Items and Better Chat unless a staff member says it's okay.
Section XI: Loopholes
Exploiting loopholes is also a bannable offence. If you discover a loophole, report it to staff immediately.
Section XII: Rule Changes
One last note, these rules can be changed at any time. Be sure to check the rules often.