Storm Sergeant First Class -> First Storm Lieutenant Promotion

[Enkidoh]

Yeah, as has been said you have to complete the Grand Company hunting log (found by clicking on your nation logo on the Hunting Log screen), and completing a quest given by another NPC at your GC headquarters, which involves running through and completing the Aurum Vale (even if you've already done this dungeon once before, you have to do it again for this GC quest).

Also there is no 'First Lieutenant' yet - the highest rank currently available is Second Lieutenant.