Natural Progression of Missions/Areas

In what order does a person visit each of the areas if they follow all of the missions? In what order are some of the notable explorable areas most easily accessed?

I ask this mainly to determine where all the skill trainer's are. On the site they're listed alphabetically however I'd like to determine more of a timeline order as to when they're normally accessed in the natural progression of things.

This was more of an issue when you could craft skill charms and could determine whether it was advantageous to use a ring and have a skill now instead of waiting until you got to a trainer much further down the road. Nevertheless, it would still give people a sense as to when their favorite skills will become available....unless of course, a boss monster casts it earlier.