I have learned one thing from productivity expert David Allen: write down thoughts, ideas, questions, or tasks as soon as you have them.
Many people focus on organizing their information and data. But first you need to collect and store your own new thoughts and ideas. You need to be disciplined about capturing them as soon as they come to mind. It's easy to create folders and wikis on your computer. It's harder to pause a conversation or meeting, or lean over to your bedside table when only half-awake, so you can jot down a thought you may need to remember.
I have pads of paper on my bedside table, on my desk, in my briefcase, and am always scribbling things down on my PDA.
Buried in a Wired article Allen summarizes this philosophy clearly:
That last sentence is true, too. In my book I talk about how most business ideas sprout forth from your "fringe thoughts" list.
Bottom Line: If you're thinking the same thought twice, in the same way, for the same reason, you're wasting time and energy. Store your thoughts / tasks as you soon as you think them.