Not sure if my methods are commonplace, or fairly unique. Probably the former. I am definitely not as organized as Jonathan, that's for sure

When I have a shoot upcoming I sit down with a spiral notebook and jot an outline of the broader subjects/concepts I would like to include. Since I am usually shooting models I will think of what types for shots these particular people will be good for.
After I get the broad categories, such as let's say - medical, business, technology - then I will come up with shots I want within each category. It is really about brainstorming. Once I devote the time and energy, the ideas just start coming.
I then go over the ideas with my hubby, and he usually has some suggestions to add that were inspired by my ideas.
I also leave room in each concept for spontaneous ideas. The models usually have some ideas to add, and some of them are good. Some aren't, but I shoot them all so they feel part of the process. Often the models' ideas are completely original because their brains aren't filled with stock cliches like mine

I may also have some new inspirations while shooting too. It is a very creative process when you are working with the models, if you make them part of the process.
I try to shoot the ideas in order of importance to me because usually we never have time to shoot everything I want. The leftover ideas I save for another time.
Of course the above doesn't apply to food, nature, or still life, but for those I still use the same process of filling out the general ideas in the spiral notebook.
Hope that helps, Warren

Forgot to add: I keep the notebook by my bed at night. Some of my best ideas come just as I am going to sleep or waking up.