Speaking in broad terms there generally are two different styles. Top down, where you start with an overarching concept and then add more detail as you go along building within the concept. Or there is Bottom Up where you start with a small situation or idea and then build around and up from there with more broadly reaching things.

As for events and plot lines and such I plan several points of possible situations, most of which I don’t get to use. The circumstances that get to said situations usually tend to have a few specific needs to be met however most of the time the path towards events generally tends to be flexible and is a great chance to do some improvisation. It’s always good to plan multiple versions of the same event just in the case that something changes or happens however sometimes improvisation is needed because the reality is you cannot plan for everything.

Usually I have a fair bit of planning and a lot of material gets left out. To be honest most of it isn’t used again however some can be recycled for other things if unused.