The beginner's box may seem like a very small amount of material to work with, but it's actually everything you need to create basic games. Here's a tip or two from my own experience as a DM, Storyteller and GM:
When in need, steal everything that's not bolted down.
In the back of the rule book (the one that says "read this last") are stat blocks for several enemies, including Minions and Nemeses. If you want to run a game where the players are facing pirates instead of stormtroopers, just steal the stormtrooper stat block and swap the name out. You can tweak one or two details rather easily to make them feel different, such as dropping their blaster ability a little to make them less "lethal" and giving them an underhanded ability to make up for, such as re-rolling one green dice once per encounter or adding a Boost if their target has already been attacked this round.
Try telling it backwards.
Take the structure of the printed adventure and use that as a template for different types of encounters, then take those encounters and mix them up. I did that below as an example:
Enc 1 (running away into combat) > Enc 2 (using skill and RP in negotiation) > Enc 3 (using skill or combat to complete mission) > Enc 4 (ambush combat) > Enc 5 (using skill or combat to complete mission) > Enc 6 (starship combat and chase scene)
What happens if you ran it in reverse order? Start the session with a starship combat / chase, then the players have to use skills to deal with the aftermath. Maybe they find a business opportunity to help cover the cost of repairs, or to deal with the threat that was chasing them.
Another thing to remember when you're planning your game: use failures to move the story forward. Figure out what happens if the players succeed or fail at something, and use both opportunities to push the game forward. Say you start with starship combat: what happens if the players get shot down? What happens if the people attacking them escape? Both might require the players to land and get repairs, but if they were shot down then they may not be able to get everything fixed before taking off again. How many times did the Millennium Falcon's hyperdrive break down in Empire, and turn what was a normal chase into something epic instead?
Good luck, and have fun!