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 <50 nodes, old items will become irrelevant, ...), keep that in mind.
Take time to read the patch notes and the possible tutorial screens. It's tiring for everyone to answer the same questions 10000 times, and it will probably help you a lot not getting lost, and even prevent you from making poor decisions. If it's like other times, the patch notes will be up way before the end of the maint anyway.
Be nice. We'll probably see the return of the quests "kill 10 mobs" with 500 people trying to kill these poor mobs, of the instanced quests where there are not enough instances available; don't be a dick, make parties for killing the mobs, try to be organized for the instanced quests and not just try to spam the NPC to hope to get it before everyone else. There's really no rush, and as on the road, chaos doesn't help anyone, it just makes it slower for everyone.
And to finish, take a few seconds to post your questions/thoughts in the right subreddit thread when HW will be launched. The moderators go through wide lengths to organize discussions with megathreads; you'll get your answer faster if you use them.
Have nice last ARR days!