This achievement is deceptive; its description is not true. A better description would be to say "Complete all Ebonheart Pact quest achievements". This is because the achievement is gained by earning the in game 'Hero of the Ebonheart Pact' achievement.
To view this achievement and see progress go to your menu (press start in game), journal, achievements, then quests (right at the bottom). In this there are general achievements, one of which is the Hero of the Ebonheart Pact quest; the one you must earn.
To earn this you must get the following in game achievements:
Stonefalls Adventurer - Complete 59 quests in Stonefalls
Deshaan Adventurer - Complete 55 quests in Deshaan
Shadowfen Adventurer - Complete 51 quests in Shadowfen
Eastmarch Adventurer - Complete 43 quests in Eastmarch
The Rift Adventurer - Complete 61 quests in the Rift
These achievements are found under the Ebonheart Pact sub-list in the quest achievements list. By viewing these achievements in this list you can see your progress.
If you are looking at this before going into the game or these areas then I suggest that you start quests whenever you see them (look for the black arrow on your compass). This means you have them available to come back to later and saves you having to find them once the area is mostly finished.
Otherwise, look for quests in major towns, there are often at least two in each. Also go to ruins and small town locales throughout the area because they also have at least one quest (often more). Also, one can find quests just by exploring the world. Caves also have quests in them (couple this with the Master Explorer achievement).
Note:
- Crafting writs do not count as a quest in the area.
- You may only have a maximum of 25 quests in you quest log at any one time, so you may need to complete some as you progress.
Thanks to GremlinLord615 for pointing out the quest limit.