Anything you damn well want.
Honestly, I don't know where I get my ideas. Sometimes I turn a little tiny nub of an idea around in my head, stretch it and bend it and flip it on its head, until it starts to form a plot. Sometimes I wake up in the morning and it's just sitting there, whole, waiting for me to pick it up in my hand like a glass bauble and make it come to life on the page. Honestly, though, I think that the people who ask this question aren't really wondering where the writer gets the ideas so much as "Where do you find the words?". I read an interesting answer to this question by Julie Norris on the 2moroDocs blog. She explained that she
always visualize[s] words up in the sky, like stars, and when writing, I just reach up and gather some. Sometimes they’re easily in reach, and other times not. Depends on the word, I suppose, or the day.I'm not sure I'm that visual, but I know there are days when the words come like a torrent, and it's all my fingers can do to keep up with the flow. And then there's days when they don't ... because sometimes they won't (to paraphrase Dr Suess).
There is a school of thought that says write every day. While I'm not sure I agree with the preachy tone of that advice, I would definitely recommend that you write a lot. And if there's a day when you don't write, at least take the time to read. As part of the NaNoWriMo frivolities, a 'pep talk' email gets sent out to participiants every few days. My favourite one this year was from Peter Carey who said, in part:
First, turn off your television. The television is your enemy. It will stop you doing what you wish to do. If you wish to watch TV, you do not want to be a serious writer.
Gin, Television, and Social Surplus. He refers to the time spent in front of television as a "cognitive surplus", and suggests that when that time is spent doing, well, just about anything other than watching television, we are making a massive change to the very structure of our society. He also argues that children are growing up in a world where that cognitive surplus is being put to much better use. Children do not see value in media that you can't interact with. While some decry this as shortened attention spans, I see it more as a shift in values. It's not so much that we require constant entertainment, or constant stimulation, so much as we ask more from our leisure time. We're not going to sit there and just mindlessly consume what's on television so much anymore. We want our leisure to be spent creating, interacting, sharing, and collaborating. This is a good thing.
If you've always wanted to write, but you never have the time ... try turning off the television. If you've always wanted to write, but you don't know where to get your ideas, or you're not sure how to find the words ... turn off the television, and take a look at the world around you. It's a hell of a lot more interesting, awe-inspiring, and wonderous than what's on the box.