You need to play through the game twice to gain all the achievements. Each achievement is won by completing a certain mission but because of the few branches in the campaign storyline it is not possible in a single playthrough. All in all 23 missions needs to be completed and several of these need to be finished twice during the course of the two playthroughs.

The guide needs to be read in a sequence and you need to select always the mission indicated by the guide. When two missions are indicated (eg. 4A or 4B) then either mission can be selected because the branch will rejoin after the mission. When the guide clearly indicates a specific selection (eg. 11A) you need to take that mission as the branches will not rejoin after this point.

I note that even after the two playthroughs there will be two missions not played and in order to play them you would need two additional playthroughs selecting the missions not played before at Mission 11. (two playthroughs are enough though for 100% achievement completion)

Thanks to Diehardsam who made most of the initial research and posted the original mission sequence in the forum section.