As others have said you should definitely unlock one of ARN's jobs asap. As for Aetherflow, use it whenever it is up. If you still have stacks when Aetherflow becomes available use them on Energy Drain. Energy Drain does damage as well as restoring HP/MP so if nothing else it can be used as an instant cast nuke. Once you Get Ruin II at 38, you can weave it in with Energy Drain for extra damage as a last resort (ie Energy Drain, Ruin II, Energy Drain). Aetherflow stacks and their management become increasing important as you level higher as a summoner or scholar, so you will want to get in the habit of being aware of the aetherflow timer. With a few exceptions, you are never going to want to sit on aetherflow at higher levels.