So the super short version is just to follow the script. You start out alongside Hien, Lyse, Gosetsu and Cirina. Follow them. At various points one of them will say something(you go on ahead, take out soandso, capture the ovoo, etc). Do as they say, follow their lead, and the instance makes it pretty clear what you need to do. If this isnt enough, then ItMe has the right of it and we need to see whats going wrong to diagnose what you need to fix.