I use Ne (I think).
I come up with ideas by brainstorming, either with myself or other people. The process is akin to word association games. Each idea has the potential to lead to various other ideas and those ideas can then give other ideas..aah a bit like nuclear fission.
If the ideas have to be generated for important stuff, it's definitely in a structured way and I'll try to stay focused, the main objectives in mind and make charts. I don't like this method, but it's how I can at least attempt to finish what I started. On the other hand, if it's for fun, then I just let the madness consume me. You never know where the ideas might take you.