Since One Tamriel, players have been able to go anywhere and do anything in Tamriel. This makes for an awesome open-world sandbox style adventure in the vein of past Elder Scrolls games, but also messes with quest and storyline continuity something fierce.
Add to this post-One Tamriel world zones from DLCs and Chapters, and the world gets very confusing for anyone who wants a coherent, cohesive, immersive storyline that spans the entire continent.
This write-up is aimed towards new players wondering "Where do I begin so I can experience the great stories that ZOS wrote into ESO without being completely lost?" I'll try to avoid spoilers as much as possible while explaining the rationale for quest order. If you just want a list of quests in order, I highly recommend this resource:
http://en.uesp.net/wiki/Online:Quests
Starting Tutorial: The starting Tutorial changes with each Chapter. If you own only the base game, you will start in Coldharbor. If you own the ESO/Morrowind, you will start in Morrowind. If you own Summerset, the most current Chapter, you will start in Summerset. There is no option to change your starting location from these places. If you skip the tutorial, you will end up in the ending region of that tutorial (Starter Island, Morrowind, Summerset, respectively.)
Getting Started
The Vestige
Important Spoiler Below for the Coldharbor Tutorial/ The Hooded Figure Quest
The Player Character becomes a soul-shriven Vestige with no soul in the Coldharbor Tutorial. Many quests in the base game zones and some quests in the Daedric Wars zones will acknowledge this. Therefore, I highly recommend that you complete this tutorial as soon as possible after starting a new character. You will need to wayshrine to the starter city of your alliance, talk to the Hooded Figure and complete the Coldharbor Tutorial quest so you can get started on that portion of the Main Quest. Starter Cities are: Davon's Watch, Stonefalls for the Ebonheart Pact; Vulkhel Guard, Auridon for the Aldmeri Dominion; Daggerfall, Glenumbra for the Daggerfall Covenant.
What if I want to roleplay a vampire/werewolf?
The shrines for vampire and werewolf are found in the Rift, Reaper's March, and Bangkorai. You can hunt for NPC mobs of werewolves and bloodfiends or you can do what I did and ask for a bite in zone chat. Many players will give a bite for free. I got mine quickly by offering to pay for it.
From there you have a choice of two major Content Arcs: Molag Bal's Planemeld or the Daedric Wars
Molag Bal's Planemeld
This arc takes up the majority of the base game zones and the Main Quest. It precedes the Daedric Wars arc chronologically.
The Daedric Wars
This arc takes up Morrowind ->Clockwork City -> Summerset Isles, though each is designed to be able to be a standalone story. This arc is after the Planemeld chronologically but can be completed beforehand with minimal immersion problems.
Daedric Wars: Morrowind, Clockwork City, Summerset Isles
Since its the most recent content, let's deal with this first.
Chronologically, the Daedric Wars happens after the player has completed the Main Quest of the Molag Bal's Planemeld Arc. It also happens after the Orsinium DLC, which has an easter egg from the end of the Coldharbor questline and another easter egg foreshadowing events in Clockwork City. Nevertheless, players can experience the Daedric Wars arc without having completed the Planemeld or Orsinium (which has very little bearing on the arc).
Morrowind, Clockwork City and Summerset Isles are designed to be standalone. I think they are better in their chronological order. Morrowind serves as an extended prologue to the events of Clockwork City.
Molag Bal's Planemeld: Alliance Zones, Coldharbor, Fighter's Guild, Mages Guild, and the Main Quest
The Main Quest starts in the starter city of your alliance when you talk to the Hooded Figure and you'll experience the original Coldharbor tutorial. This will dump you on your alliance's starter island(s). Starter Cities are Davon's Watch, Stonefalls for the Ebonheart Pact; Vulkhel Guard, Auridon for the Aldmeri Dominion; Daggerfall, Glenumbra for the Daggerfall Covenant.
From there, the pre-One Tamriel order goes like this:
Starter Island(s)
1st Zone (start fighters and mages guild, start Haborage quests for Main Quest, writ certifications, etc.)
2nd-5th zone, doing fighters guild, mages guild, and Main quests as you level up, until you've finished your alliance, guilds, and stopped getting Main Quests.
When you get the "Messages Across Tamriel" quest, you'll gather the 3 faction leaders and prepare to assault Coldharbor
Do the Coldharbor quests. These are prerequisites for completing the Main Quest.
Complete the Main Quest
Talk to Cadwell about doing Cadwell's Silver and Cadwell's Gold which are the other faction's questlines.
Alliance Zone Order
Ebonheart Pact has a fairly fragmented storyline, but there are a few events that will only make sense if done in order (technically Deshaan and Shadowfen could probably swap around without a problem).
Chronological Order: Bleakrock Isle -> Bal Foyen -> Stonefalls -> Deshaan -> Shadowfen -> Eastmarch -> The Rift
Daggerfall Covenant is also fairly fragmented, but has more characters that carry through from zone to zone. (Technically, Alik'r Desert could be done at any time after Stormhaven, story wise.)
Chronological Order: Stros M'Kai ->Betnikh -> Glenumbra -> Stormhaven -> Rivenspire -> Alik'r Desert -> Bangkorai
Aldmeri Dominion has a very coherent and cohesive storyline with tons of recurring characters. Please do this questline in order or you will be very confused.
Chronological Order: Khenarthi's Roost -> Auridon -> Grahtwood -> Greenshade -> Malabal Tor -> Reaper's March
DLC and Other Zones:
- Cyrodiil: Cyrodiil is a PVP zone, where the quests are very simplistic and have little to no story, due to the risk of fighting enemy players. It happens concurrently with the Planemeld and before the White Gold Tower dungeon.
- Imperial City: the Imperial City is a PVP zone with a PVE/PVP main quest. The main quest will involve questing in PVP-enabled areas with lots of miniboss NPCs. White Gold Tower dungeon makes a nice conclusion to the IC main quest (though that dark anchor still doesn't close.)
- Craglorn: Craglorn is part of the base game but has its own problems apart from the Daedra. Several parts of the quests strongly advise getting a group of players together to complete them.
- Dungeons and Dungeon DLC: aside from White Gold Tower, none of the dungeons have any impact on the storyline as a whole
- Gold Coast: Gold Coast happens after the Planemeld and has recurring characters from all three Alliance storylines
- Hew's Bane: happens after the Planemeld, I don't believe it has recurring characters from the alliance storylines?
- Orsinium: happens after the Planemeld and before the Daedric Wars Arc. This has an easter egg for something at the end of Coldharbor and an easter egg foreshadowing Clockwork City and coming after the end of the Main Quest. I highly recommend doing Orsinium after doing the Daggerfall Covenant questlines.
So what if I really miss or want to have the pre-One Tamriel Questing Experience?
1. Start a new character and wayshrine to your Alliance's Starter City
2. Accept the Main Quest from the Hooded Figure
3. Complete your Alliance's Main quest in order alongside the Fighters and Mages guild quests for that zone, and the Harborage quests for the Main Questline. Originally the Main Quest progressed at every 5 levels, but now its not necessary to wait.
4. Coldharbor Questline is the prerequisite for completing the Main Questline.
5. Having completed the Main Questline, accept Cadwell's Silver and Gold to experience the other Alliance questlines.
6. Experience the Thieves Guild, Dark Brotherhood, Imperial City, and Orsinium DLCs and Craglorn, in whatever order you want.
7. Begin the Daedric Wars plotline with Morrowind -> Clockwork City-> Summerset.
Its entirely possible to have a great and fullfilling questing experience running around doing everything in whatever order you want. Its an Elder Scrolls game in that regard. If, on the other hand, you want to experience the coherent, cohesive, immersive storyline of the Elder Scrolls Online that spans the entire continent for the first time since TES: Arena, following the chronology of the original pre_One Tamriel ESO through the threat of the Planemeld and onto the rising threat of the Daedric Wars is one of the best ways to do so.
I hope you have fun questing through ESO's story arcs!