Did you visit all 3 main cities as envoy? If not then yes get airship to gridania. To do so go speak to the lift guy at bulwalk, lift to airship landing and speak to the ticket seller who should have a story quest mark overhead.

Or you can check out this link of quests and find where you got up to and carry on from there:

Mainstoryquests page2

( Btw incase you can't remember which you've completed, go you your journal and click the 2nd tab to show completed quests, use the drop down to find story quests you've done. )