More than simple plot hooks or adventure seeds!
A premise is the heart of a story summed up in a single sentence. It will provide a general overview of what happens, without spoiling anything. A good premise contains, explicitly or by implication, four key elements of the story: who the protagonists are, what the goal of the story is, the sorts of obstacles that need to be overcome to achieve the story goal, and who the antagonist is.
Each premise provided in this book is more than just a story hook or adventure seed. It is the beginning of a story, your story, that you can flesh out and develop to suit your specific needs. These can be used again and again by varying the details and changing the four key elements.
The assumption is that you already have player characters created, if not fully established. For that reason, elements of the premise should be tweaked to suit the abilities and personalities of the protagonists and not the other way around. Suggested character capabilities useful in completing the story goal may be listed, but if no protagonist possesses these traits then a supporting character should be inserted to compensate. Likewise, ties to background elements can either be retconned into a protagonist's history, or given to a supporting character who can ask for the protagonists' help, or hires them to pursue the story goal on their behalf, as appropriate.
The story goal is the objective that the protagonists must achieve in order to successfully complete the adventure. It’s the way you know that the story is over, and can help keep the players focused and the protagonists on the right track. In a simplified 3-act structure, Act 1 will have the protagonists learning about the story goal and deciding to pursue it. Act 2 will present a series of obstacles that need to be overcome in order to accomplish the story goal. Act 3 will have the protagonists face the final obstacle, defeat the antagonist, achieve the story goal, and earn their rewards.
Achieving the story goal shouldn’t be easy, and the protagonists will need to overcome an escalating series of obstacles. These might be linked thematically, or tied into the sort of goal that needs to be achieved. Start with a simple obstacle early in the story, something that plays to the protagonists’ strengths and will be relatively easy to defeat. Then think of the hardest thing possible, pushing the limits of their capabilities, and make that the final obstacles. Flesh out the middle with obstacles that are increasingly more difficult.
Each protagonist has a personal goal that they are trying to achieve, as well as a motivation for pursuing that goal. This might place them in opposition to, ior nto competition with, the protagonists. If the premise fits with an established antagonist, you should use them and tweak other elements of the premise to fit their personalities and abilities. Otherwise, you can create a new antagonist that suits the particulars of your desired story and overall campaign needs.