My approach to campaign design is generally to create factions and NPCs more than anything. I will pick a starting world for the campaign and start detailing in the various factions for each world as my intuition leads. I tend to make sure the factions within the local government are covered, any significant criminal organizations, any important religions, any Imperial Nobles who have fiefs on a world, any major business interests, and anything else I can think of. Usually, when I create a faction I write a little about their ideology and goals and usually create a faction which is against the first faction entirely or in part. Competition and conflict make good stories. I try to make any local Scout or Naval bases factions of their own, along with the local Starport Authority. A paragraph on each faction is enough to get started.
After creating factions, I start creating important figures in each faction. Usually 2 or 3 is enough for each faction and you don't even have to do but a rudimentary description of them. What matters is their individual ideology and motivation within their faction. Some NPCs within in a faction might be rivals or even enemies.
The faction and people creating process makes it easy to create adventures. Even if you do a 76 Patrons/Amber Zone style adventure, you already have some framework. If you're patron is a retired pirate who had his now legit business raided by armed assailants and wants to know who did it so he can take revenge, you can draw on your factions. Who might a pirate have angered who would take this sort of revenge on him? Well, this business faction A might be someone whom the pirate stole a cargo from years back. Person X in this business faction already has a vindictive streak and little respect for laws. There we go. There is the who-done-it and why. Maybe the raiders who hit the pirates business were a special ops group from Mercenary faction D? I have already written how they have teams of covert ops who do not operate in a strict military manner, and who do jobs that might be illegal. The rest is locations and lesser NPCs.