Expedition Leader

You don't need group for this achievement anymore.
You can just talk to [npc=123000] for Horde and to [npc=131290] for Alliance (instead of clicking on the table) and queue for mythic solo version and do all of this.

also pvp achievements are removed from this meta achieve

I've completed this achievement somewhat early this expansion, and thought I'd share my tips with everyone for each achievement so that you can become an Expedition Leader like me!

General

Azerite Admiral
This is more of a time-consuming achievement that you'll simply get eventually by completing island expeditions on any difficulties. It is worth noting that this achievement is account-wide progress, meaning that you can work on it with any of your characters. Losing an island will still get you credit towards the achievement. To throw some maths in here, you will need to win either:

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• 167 Normal islands (6k each) or;
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• 112 Heroic islands (9k each) or;
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• 84 Mythic islands (12k each) or;
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• 56 PvP islands (18k each).
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Metal Detector
This is arguably the easiest achievement and you get it by looting 100 [currency=1710]. Those are commonly found in bags such as the [item=163612], that you can receive at the end of an island expedition, and can sometimes be found on the ground in your expeditions. They are small gold coins that are very hard to see, so keep your eyes opened!

Give Me The Energy
For this achievement, you will have to pick up 30 azerite orbs that spawn on the ground when you defeat elite and rare creatures on the islands. To collect them, simply walk over them. This will heal and buff nearby allies.

Team Deathmatch (Alliance) / Team Deathmatch (Horde)
To obtain this achievement you will have to defeat every AI teams. It's totally random which team is gonna be playing against you, so this may take some time to complete. The AI are fairly easy to kill, and can even be soloable depending on gear and difficulty. This can only be done on Normal, Heroic and Mythic difficulties.

Rare

I'm Here for the Pets
This achievement requires you to loot the 28 original pets from island expeditions. You will get pets and different rewards based on what types of creatures spawn on the island. For instance, [item=163798] will only drop if there are pirates on the island. It is worth noting that you can loot the same pet multiple times and this achievement is account-wide progress. You can also buy them from the auction house or obtain them from the crates such as [item=173991].

Tell Me A Tale
To get this one, you need to loot 20 quest items and complete them. You will get these depending on what spawns on your expedition. For instance, [item=163470] can only drop if there's a mogu invasion. Turning a quest will give you 700 AP, and completing all 20 will net you a whopping 14000 AP and the achievement. You can only loot a quest item once per character, but the achievement is account-wide progress.

Helping Hand
For this achievement, you have to rescue the 25 NPCs that can randomly be found on islands. Those NPCs will be marked by a ! on your map and to save them, you need to get an item that is usually somewhere around the NPC, and interact with them. You can easily find them using the [item=151114], otherwise just keep an eye on the minimap. This achievement is also account-wide progress.

Mythic/PvP Only

Expert Expeditioner
This achievement starts as [achievement=12596], then turns into [achievement=12594] and finally Expert Expeditioner. You will have to win 50 Mythic island expeditions on a single character.

Notorious
This achievement starts as Bayside Brawler, then turns into Blood in the Water and finally Notorious. You will have to win 50 PvP island expeditions on a single character. It is worth noting that you won't necessarily have to engage the other team to win, and I don't recommend doing so. Best strategy to win PvP islands is to simply collect as much azerite as possible and hope to do it faster than the other team. You should only engage in PvP if you're sure to win the battle, otherwise, try avoiding it at all costs.

Island Conqueror
This achievement is earned once you have won every single islands on Mythic difficulty. There are always three different islands that you can queue for, and they rotate every resets. This will take a couple of weeks to achieve. This achievement is account-wide progress.

Island Slayer
This achievement is the same as the previous one, except you need to win them in PvP difficulty. It is also account-wide progress.

General tips

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• The best and fastest way to clear islands is to have one or two people mount up and pull as much as possible while the other(s) collect chests and azerite behind, then meet up somewhere and AoE everything down. This kind of strategy usually involve having a tank + two DPS or simply three DPS.
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• Don't feel too bad for not receiving credit for a specific achievement after an island because you're still rewarded with a decent amount of AP, transmogs and pets (which can be sold at the auction house for gold), mounts, and dubloons to buy even more transmogs and pets.
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• Speaking of dubloons, make sure to buy items from the boat vendor such as the [item=163765], which can help a lot clearing islands.
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• As mentioned above, try to avoid PvPing for the PvP achievements. It'll most likely be a waste of time for both teams. If you really want to sabotage the other team, you should try getting a rogue in your group to steal their chests/azerite sources, or if you're confident enough, you can try stealing their tags if they're mass-pulling while mounted and burn down everything before the other team kills you.
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This will become one of the rarest titles in the game.