Here is a vague outline of the order of quests in ESO;

Main Quest/Faction Quests/Fighters Guild/Mages Guild

These quests will take you through the starter tutorial as well as the main story line of ESO. The original guild and faction quests run alongside this and will give you additional lore and experience.

1. Chapter Tutorial / MQ Start
2. @ Lvl 5 – Harborage Quest / Faction Quest / Fighters Guild / Mages Guild / Undaunted
3. @ lvl 10 – Harborage Quest / Faction Quest / Fighters Guild / Mages Guild / Undaunted
4. @ lvl 20 – Harborage Quest / Faction Quest / Fighters Guild / Mages Guild / Undaunted
5. @ lvl 27 – Harborage Quest / Faction Quest / Fighters Guild / Mages Guild / Undaunted
6. @ lvl 34 – Harborage Quest / Faction Quest / Fighters Guild / Mages Guild / Undaunted
7. @ lvl 38 – Harborage Quest / Faction Quest / Fighters Guild / Mages Guild / Undaunted
8. @ lvl 44 – Harborage Quest / Faction Quest / Fighters Guild / Mages Guild / Undaunted
9. Cadwell’s Silver / Undaunted – This is a quest you will be presented by Cadwell on completion of the main story arc which allows you to “go back in time” and see what would have happened if you had washed up on the shore of a different faction. Depending on your starting alliance will determine which you will go to next.
10. Cadwell’s Gold / Undaunted – This quest is much like the last, and give you access to the questline for the third alliance.

Early DLCs: Imperial City, Orsinium, Thieves Guild, Dark Brotherhood

1. Imperial City / Undaunted.
2. Orsinium.
3. Thieves Guild
4. Dark Brotherhood
5. Shadow of the Hist / Undaunted – Cradle of Shadows and Ruins of Mazzatun

The Daedric Wars

1. Prologue Quest – The Missing Prophecy
2. Morrowind
3. Horns of the Reach / Undaunted – Bloodroot Forge and Falkreach Hold
4. Prologue Quest – Of Knives and Long Shadows
5. Clockwork City
6. Dragon Bones / Undaunted – Fang Lair and Scalecaller Peak
7. Prologue Quest – Through the veil Darkly
8. Summerset / Psijic Order
9. Wolfhunter / Undaunted – March of Sacrifices and Moon Hunter Keep
10. Prologue Quest – Ruthless Competition
11. Prologue Quest – The Cursed Skull
12. Murkmire

Season of the Dragon

1. Wrathstone – Depths of Malatar and Frostvault.
2. Prologue Quest – The Demon Weapon
3. Prologue Quest – The Halls of Colossus
4. Elsweyr
5. Scalebreaker / Undaunted – Moongrave Fane and Lair of Maarselok
6. Prologue Quest – The Dragonguard’s Legacy
7. Prologue Quest – The Horn of Ja’Darri
8. Dragonhold

The Dark Heart of Skyrim

1. Harrowstorm / Undaunted – Icereach and Unhallowed Grave
2. Prologue Quest – The Coven Conspiracy
3. Prologue Quest – The Coven Conundrum
4. Greymoor