Hey! I think that everyone is pretty hyped for Heavensward, so, just a few tips before the maintenance.
Stop planting new high-level plants right now. They will probably die during the maintenance.

Do NOT disconnect in Coerthas. Do you remember what happened with Gold Saucer? People logged off inside it on first day, people who had their Home Point there, who all couldn't play because the Gold Saucer area was too full to accept them when they wanted to come back. So, as much as you want to save these 30 seconds to start the new story quest, do yourself a favor and disconnect somewhere else. We don't know how stable the servers will be, and you probably prefer to be able to play and do something else while trying to teleport to Coerthas, than just being stuck on the login screen.

Stock up on stuff, prepare your sales. Many things will probably have huge prices changes (people will gather less lvl