I don't tend to struggle coming up with ideas for story plots - the 'one sentence summary', as it were. As soon as it comes to breaking that into a series of events and chapters, though, I quickly get stuck. I know who the main characters are and what problem they're walking into, but when I have to decide what follows from that inciting incident I never know what to do next. Does anyone have any good advice for creating the story timeline?
There are a number of different frameworks for writing stories. You'll have to try as many as you can to find what works for you. This is but one method.
Yes, but / No, and
Any time your characters try to overcome a problem, it will have one of two outcomes: "Yes they succeed, but a complication arises", or "No they don't succeed, and the consequences of that failure occur."
Yes they killed the attacking zombie bear, but now they have no ammo left.
No, they failed to ford the river, and now they're soaking wet in the middle of winter
Yes they managed to dry their clothes off, but their fire attracted bandits
No they failed to steal more ammo, and now there is a warrant out for their arrest.
Yes he managed to win her trust, but now he has to pretend he's an FBI agent
No she failed to reconcile with him, and now he won't speak to her.
A good story will have a mixture of both. By considering the consequences of success you naturally move the story along to a new conflict after the previous one resolves, and considering the prices of failure make sure that the story progresses even as the characters face roadblocks.
Start with some small obstacle, and then run your story until you reach an end.
If you're having difficulty thinking in this format, try analyzing an existing story in this style.
Yes the Millenium Falcon reached Alderaan, but it isn't there anymore.
No they failed to escaped the tractor beam, and now they're stuck on the Death Star.
Yes they rescued Leia, but now all three of them are cornered.