A campaign differs from everyday posting by its goal: fill weekday tables, sell out a class, launch a product. Every post in it has a job in getting there.
Plan it backwards: the goal, the people who need to act, what they need to hear, then the posts and dates. Choose the KPI before the first post, not after the last.
Example
A café's three-week campaign to sell a new breakfast menu: a teaser, the dishes one by one, a regular's review and a weekday discount.