Almost all of the ideas I have stem from problems in my life and work. Ideas I have on a topic accumulate slowly, and eventually reach critical mass. At that point, I think I have enough to make a coherent post. I might suggest first getting into the habit of incubating your ideas in some system, whether a set of text files under version control like I have or Evernote or whatever works for you. You'll make a lot of connections this way that you would otherwise not make. (Unfortunately I have almost no time to turn my semi-organized outlines into posts at this point, but that's life.)
Some of my other ideas are responses to other things I've read. For books, writing a book review or summary (especially if it includes a bit more than is in the book, i.e., other things you are aware of) might be a good approach for this. Replying directly to things you've read online also is pretty easy.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
Notes for future OT posters:
1. Please add the 'open_thread' tag.
2. Check if there is an active Open Thread before posting a new one. (Immediately before; refresh the list-of-threads page before posting.)
3. Open Threads should be posted in Discussion, and not Main.
4. Open Threads should start on Monday, and end on Sunday.