I'm not sure if I can help.I don't know if I have any particular method. I'll try to suggest a few things. I read a lot in things that interest me and often run into ideas in books that I can further research.I like to browse in the library at times until something grabs my attention.At times I go to old stuff that I have done and try for a different approach.It is sort of a state of mind to recognize possibilities when you find them.
With the series of towns I am writing I will sometimes just take a map and choose a town, research it and write about it.
Don't know if this will help you.