Main or sidequests

[Harle]

Is there a way to distinguish between main and side missions?

[Noobiecanoobie]

Sometimes the mission map has more than one choice and the text describes the mission as optional.

I think the optional missions also have a different color map marker.

EDIT: Just read an old post, the Dev says optional missions remain on the mission selection map until near the end of the game, so you can do them in any order, perhaps later when you are better equipped.

[lionhart]

Main missions are marked with green nodes on the map, and side missions are the yellow nodes. And yes, you can skip the side missions and come back to them later when you are better equipped. That might be a good choice because it seems like the side missions are a little tougher than the main missions.