In order to define my ideas, I think I want to clarify the statement to be "How or where do you get your ideas?" The basic summary answer is "I read, I listen, I watch and I think."
Read everything that you can. Fiction, non-fiction - it doesn't matter. The bigger the range, the better, although I do place a lot of value on reading non-fiction in order to a) learn more about the world and b) add an extra dimension of depth to your work. Obviously it helps if you have a vague interest in the subject to start with, but try reading about something new. A throwaway line or footnote in a non-fiction book might just prompt an idea that might work for a flash, or it could be expanded into an entire novel. My historical horrors (e.g. The Resurrection Men, The Hidden) are usually inspired by things I read in non-fiction books, and it's the extra material gleaned around the central concept that provides the "oomph" for the stories to work. Without the knowledge, there is no idea. (I wrote more about this when writing about historical fiction)
Likewise, reading genres different to those in which you normally write can be invaluable for providing ideas. If you usually write sci-fi, try hardboiled thrillers. Maybe you can write hardboiled sci-fi! If you write romance, give steampunk a try. The new ideas you encounter might just spark off some of your own.
A writer is often a covert eavesdropper. Even a fragment of conversation can provide the seed of an idea. The writer can plant that seed and watch a throwaway line bloom into something they can use. If you channel surf at home, listen to the strange, disjointed sentences formed as you go from one channel to the next. Is there a prompt or even a plot in there? When you're listening to music, pay attention to the lyrics - do the songs tell a story, or do they simply inspire a plot in you? (Unforgettable, by Nat King Cole, did that for me).
I firmly believe that if you're willing to find ideas anywhere, then you will. Don't walk around with your head down, ignoring the world around you. Look at advertisements. Watch how people interact (but don't be obvious about it!) If you read the paper while commuting, pay attention to headlines. Read the 'Wanted' ads or personals columns. Even look at the problem pages - what could explain the erratic behaviour of Upset in Bristol's husband, aside from the obvious? I even wrote a post about this way back in January - check out my Creativity game!
Make a list of the top ten cliches that most annoy you, and then think of a way to subvert them. Choose a character from either a work in progress or a finished piece, and then write down your top five most embarrassing moments - how would your character react in those situations? Think about the professions you wanted to do when you were younger and write about one of them now. Choose a favourite movie and think about its structure. What other stories could you tell using the same structure? Think about the plot of a finished piece, and consider how the plot would run if you told the story backwards. Finally, find a source of writing prompts (Eric J Krause runs them on his blog, as do Write Anything and Writer's Digest, while I've started a series of weekly photo prompts, starting with Old Bear) Can you combine two or more prompts to give a new plot?
If you exhaust these possibilities and need more ways to find ideas, Marelisa has some up on her Abundance blog. Take ten minutes to create something...and enjoy yourself!