This achievement is pretty easy to get along the way when playing through the story. In each area you will find the following things that will show the location of other collectibles in the area. Although they can be found without these, it makes them much easier to find by revealing them on your map.
All collectibles in the area
All loot in the area (Survival Caches)
Monoliths: Reveals coin caches.
Please note: Some collectibles can only be obtained after proceeding forward with the story then travelling back to a camp further back because you can only travel so far back on foot. Syria can be travelled back to after completing the story.