We have a massive world here, and thus, we need a special method to keep things running properly.

No man has the ability to be in two places at once. You can't be in the emperors court in the fire nation, and a teashop in Ba Sing Se. When you leave one place, make a post that shows that, before going elsewhere. Do not post in two IC places at once.

When traveling, keep in mind that locations are very far apart, and make appearances in at least a few of the places in between your destination. You can't walk out of the king of Omashu's palace and straight into the northern water tribe.

If you have to go someplace requiring special methods to reach, such as an air temple, or an island, do not simply appear in the new location without telling how you got there. Swimming across the ocean to an island is a bad idea, there are sharks, and sea monsters. You need to find someone with a boat. Do not create your own NPC for this purpose either, let someone authorized do it.