Recommendations:  If this is your first time on the Plane of Sky this is a good starting point. It is suggested that you bring Ar gear, in particular, for your main tank. Ideally it shouldn't take you more then a few hours to successfully navigate through the chain. It is recommended your war party be composed of 5-8 level 60s.

Before porting to the Plane of Sky assure that each player has 2,000 to cover the cost of the key. Once you have done so, port up and purchase the rain key from the merchant.

Approach the essence of the rain and wait until you receive a pop-up. Do not have everyone rush the essence as it does take a few minutes for the pop-up to reset. Read the text carefully to insure that you do not accidentally decline the port.

Island 1:You will appear under a stone acheway and be greeted by a pop-up which essentially welcomes you to the Plane of Sky. The mobs on the small island con light blue to a level 60 and are fairly week. They have an Ar nuke without an AoE. With a war party of about 4-8 level 60s they should not be difficult. Travel along the edge of the island and survey it for a named mob. Defeating the named mob will drop 8 keys which will allow the party to continue to the next island. The keys are not NTL items and can be distributed to the party. A portal will spawn in the center of the island, so assure you have a clear path to it.

Island 2: Once you have arrived on the island speak with one of the fairies and log the quest. In order to log the quest you can not have more then -99 faction with the appropriate fairy faction. Only one person can do the quest at a time, but more then one can have it logged. She will tell you that her daughter has disappeared in the maze and asks that you find her. To navigate through the maze go left and then forward when you reach the bend and duct in right. In order to reach the exit successfully you may have to back-track, as it is easy to get lost. Just be cautious of the gargoyle guards and attempt to deal with each on a single term basis. When the player with the logged quest approaches the girl on the other side of the maze a mob which cons yellow to a level 60 will spawn.

Once you have done so you will need to return to the guest NPC in order to acquire a wand which will allow you to craft 8 keys to advance to the next chain. In order to avoid spending an unnecessarily long time on this island you might want to consider "farming" the gargoyles until they drop a loot item in order to make the trip back and forth easier. Give each member of your party a key and advance to the next island.

Island 3: For those of you planning to do the Plane of Sky armor quest, this is where you can locate the NPC quest giver. The NPCs are located in the aviak village. Speak with all of them to determine who is yours. Also log the island quest in order to advance to the next island.

The quest NPC will ask you to return with 4 feathers from the appropriate mob. Farm them with your war party until you acquire the feathers. The NPC will then send you into the underground cavern. Be cautious of the maggots and try to coordinate your war party so that they don't accidentally descend the sudden drops and land on a hostile mob. When you approach the last drop try to descend to the right. Send your tanks down first. If you do wipe, try to have everyone reconvene on the right side of the cavern to coordinate a battle plan. Clear the room and fight the main mob. Have the person whom has the quest logged loot the drop. Defeating the mob also spawns a portal out of the cavern. Once the item has been returned to the NPC the character will receive a wand which can be crafted into 8 keys. Approach the portal located near the Aviak village and advance to the next island.

Island 4: You will appear on an island inhabited by small demons. Circle around the side of the island to the other side and roam around the area until you acquire a pop-up which will spawn a warlock Aviak. Defeating him spawns the portal to the next island.
The following suggestion was taken from the main boards:

Island 5: If you are working on the level 57 Lava Storm quest run to the right to receive the pop-up. If you are working on the level 59 Lava Storm quest go to the left. Otherwise, prepare your war party for battle with the Chimerean Tyrant! Determine who you wish to be "flagged" and have them group together in what you assume will be the kill-group. Have the rest of the war party remain solo or grouped with a rezzer. The Tyrant does not have an AoE and should not be difficult if your war party is prepared. When he is defeated a portal will appear. Advance through it and speak with the manifestation of rain. If he speaks with you, you will know you have successfully be flagged. Congratulations you have now completed the Chain of Rain!