Overview
In FFZ, "Adventures" are the individual missions within an arc and a campaign that the PC's embark on. Each one is generally fairly specific and self-contained: save the princess, protect the caravan, retrieve the holy book, kill the monster, etc. You can think of these something like quests given out by NPC's, or missions on a notice board. There is something that needs to be done, and heroes (or at least mercenaries) are required to do it.
As befits the "hook and line" philosophy, there should be more potential adventures in the game than your party will ever engage in. This shouldn't be overly difficult to achieve. It's up to the characters (and the players) to decide what they'll undertake. It's up to you to give them something exciting and significant with their choice.
Adventures in the Timeline
In the campaign timeline, adventures compose arcs (about 4 adventures per arc), and are composed themselves of sessions (about 3 sessions per adventure). Adventures stretch out over multiple sessions, and are the basic unit of advancement in FFZ: pass an adventure, and gain a level. They are conflicts that take a few in-game days to resolve, but that are rather self-contained, tying into the ongoing campaign briefly. Each adventure should follow the last in the narrative chain: Beginning, Middle (two adventures for the Middle), and End, repeating the cycle as the next arc begins.
Adventure 1 (Arc 1)
(Sessions 1-3)
This is the introductory adventure, and should focus on the main characters, introducing them, their first base of operations, and the first big enemy (who also has links to the major villain, though these may be obscure at this point to the players).
Adventures 2-3 (Arc 1)
(Sessions 4-9)
These adventures should introduce other major aspects of the world or the major groups and conflicts of the campaign. For instance, if the campaign theme is Nature vs. Technology, Adventure 2 may explore Nature's role, while Adventure 3 may explore Technology's role. If the campaign is taking place in the context of a great imperial war of expansion, Adventures 2 and 3 should show both the empire's ruthelessness, and how people are resisting it. Sub-plots may be peppered into the individual sessions of these adventures, or as plot points for them: if the Nature vs. Technology campaign is also a campaign about love, for instance, themes of caring, compassion, and deep relationships can feature prominently in both the Nature adventure and the Technology adventure. Here, you may also have early bonus dungeons, giving the party a leg up.
Adventure 4 (Arc 1)
(Sessions 10-12)
Tie together the introductory session by re-igniting the major conflict of the campaign. If the villain has stayed in the background, this is a good time for evidence of its presence, influence, and plans to begin to crop up. Bring all the major allied forces together, and tie up any loose ends you don't want haunting the campaign past this point. You should have cemented in large part the forces that are at work in your campaign, so if there's any left, you may want to link them into this adventure.
Adventure 5 (Arc 2)
(Sessions 13-15)
As the middle section begins, the PC's should have a taste of what they're up against. Adventure 5 could test out some of the early theories for beating him, or could explore the villain in a little more detail, revealing potential goals and how those goals tie into the themes of the campaign.
Adventure 6-7 (Arc 2)
(Sessions 16-21)
You should begin challenging the player's archetypes, fears, goals, and other relevant questions at this point. You may introduce some character-specific sub-quests or bonus dungeons with extra rewards here, giving players who plumb their own depths a concrete reward in the form of more levels or better equipment. The weaknesses in the chosen character's philosophies should be found and probed, and the characters should be facing the central question of the narrative: do they change and grow, or stay the same? This should also link the villains to each character, however distantly.
Adventure 8 (Arc 2)
(Sessions 22-24)
Finish up the second arc by tying the players together again, in a way that recalls their first adventures together. Perhaps they face a similar enemy, or have a similar set of motives as when they first met. This should re-enforce the party bond, to ensure that they are all dedicated to each other after having their own personal moments in the previous adventures. Have them show and display their changes, or their lack of changes, in flagrant ways.
Adventure 9 (Arc 3)
(Sessions 25-27)
As the third arc begins, the villain comes sharply into focus. Perhaps it succeeds in some key part of its mission, or perhaps the great evil manages to rip apart some of the strength the party has built over the last arc. Body count can be effective, but any major disaster or defeat for the forces of good will be noticed, and will be a call to action — this evil must be stopped.
Adventure 10-11 (Arc 3)
(Sessions 28-33)
These two adventures should focus around assaulting the final villain — finding and raiding his lair, or marshalling troops and pitting them against his army, or discovering the location of the final ritual that will transform him, and trying to stop it. Ideally, this uses knowledge and character-based narrative positions that the PC's gained in the previous arc, using their in-character link to the villain to find and try and thwart the wickedness. This is also a solid place for bonus dungeons — many FF games open up very wide just before the final assault on the final lair.
Adventure 12 (Arc 3)
Sessions 34-36)
The final raid on the final dungeon, with the major villain of the campaign at it's heart, should re-inforce the grand themes of the campaign. Whichever side the heroes are on, they should be facing their antithesis here, having already confronted the evil in themselves.
Mission Templates
Though the exact types of adventures your party can undertake are entirely limitless, the actual structure and purpose of the adventures usually fits into one of a few pre-defined formats. These are essentially "adventure archetypes": tried-and-true formula for a good adventure that you can add your own individual, unique, and special world-specific touches to. These templates can be combined and re-mixed in order to create more complex adventures, as well.
Fetch
A "fetch" mission is one where the party heads into dangerous territory to retrieve something. It may be an item, a person, a creature, a plant; medicine, a rare pelt, a missing princess, or a rare crystal. Really, the exact item doesn't matter so much — it's often referred to as the "MacGuffin." The MacGuffin is, essentially, whatever you must go get and bring back. These are some of the most common types of missions, as they provide a reasonable pace from peace to danger and back again, with a climax right at the item in question (or upon trying to leave with it).
Escort
An "escort" mission is one where the party must guide some non-combat units through dangerous territory. This may be a caravan, a scholar, a creature, or almost anything. The escorted object is something that the enemies desire (or desire to destroy), and protecting it serves to complicate matters and make encounters interesting. When planning an escort mission, you should consider what the escorted thing can provide in encounters, and how to keep it "out of the way" except when threatened. The easiest way to do this is to give the escorted thing an "ally ability" that it uses in combat, and to have it threatened whenever a PC is KO'd in combat. It should be possible for the party to fail this mission without being KO'd themselves, so ambushes and greater numbers on the enemy's side are all important strategies, and the escorted thing must be target-able. The PC's must also have a way of preventing that targeting at some cost to themselves (such as spending a turn hiding the escorted thing). It should be noted that "defend the castle"-style missions are technically escort missions: the thing escorted just doesn't go anywhere.
Stealth
A "stealth" mission is one where you must get through a dangerous territory that you have no real hope of overcoming in direct combat. Not being able to fight your way through, you must sneak, getting under and behind defenses rather than tearing through them. Stealth missions are generally more Exploration or Trap based missions (with perhaps some Dialog encounters thrown in when under disguise or when finding allies) rather than combat-based missions. Combat should be basically deadly, something the PC's want to avoid except on a limited and ambush scale. For stealth missions, try to avoid the "one failed encounter kills us all" motif. This is too binary: there should be some room for failure before total failure (and lots of room for successes before total success). Give PC's a way to be noticed and then silence the thing that notices them before the whole thing is lost.
Assassination
An "assassination" mission is a one where the party must kill some specific entity. Either through stealth or through basic combat and straight-up warfare, that entity must be rendered dead. Frequently, PC's will get this mission against monsters, especially leaders of monster armies or rulers of monster kingdoms or especially horrible, violent, or unpredictable monsters. Of course, they might also get this mission against royalty or townsfolk and usually, the final adventure qualifies as this with regards to the villain: kill the bad guy.
Timed
A "timed" mission is generally something you add to another mission to up the tension. A timed mission adds a time limit onto the challenges, meaning that if you take too long (seconds, minutes, days, or weeks, depending on the scale of the adventure) you loose. The goal you need to accomplish before time runs out generally depends on the other kind of mission you're taking on: a timed assassination mission means that you need to kill something within a certain amount of time, for instance.
Numbered
A "numbered" mission is something you can add to another mission to up the complexity. A numbered mission adds a quantity of times the task must be done, meaning it will take longer than doing it once. Killing a certain number of creatures, or collecting a certain number of items, or saving a certain number of NPC's, can all be numbered missions. Having a numbered mission
