I’ve found the following tricks useful for Fate campaigns (running more than a few sessions).
Framing — Narrative is a powerful thing. If the PCs start out as privates in the army and get promoted as the campaign marches on to sergeants, then the scale of influence they have has dramatically expanded.
Another use for framing is the scale of effect of things. My group started as a bunch of lower-tier magic users on a college campus. Shooting bolts of energy would bust a lamp or dent drywall. Now, years later that same bolt literally sheared the front off of an apartment building.
Change stunts and aspects — As the storyline progresses encourage players to change these to be more relevant to what is going on and what the player has learned.
Looking into my Father’s Past turns into My Father was a Bad Man which turns into My Father’s Redemption is in this Journal which turns into…. well, you get the picture.
Change Stress Tracks — Keep the PCs on their toes by changing up what stress tracks mean in the narrative. Remove physical and have only social and wealth tracks for an intrigue storyline. Add a timer stress track to countdown to Armageddon.
By changing stress tracks to keep the players engaged by keeping them a bit off balance. Characters built for fighting have to figure out how to navigate social situations. Characters who love to research can’t when the world is going to die in an hour.
And really the key is … to keep the players updating their character sheets. If they’re using the same aspects and stunts they wrote in the first session in the 20th session, things feel stale. But if they’ve cycled through 4-5 different versions of their character they will feel progress.
FYI, this was originally posted to the Fate Google+ Community as a reply to the question Have any of you had success with a longer-term “campaign” game in either Fate Core or FAE?