Do not look for "how-to's" or "walkthroughs", you might find an exploit that ruins the mechanics of the whole game; fortunately I found out after I had already finished the campaign.

Also check your mission "book" after each battle. In my gameplay, the game skipped two optional missons automatically that were crucial for the plot (unless I pressed something without noticing).

Excellent variation on the turn-based strategy games, and the story is really interesting.