Don't think it! Ink it!
Ideas tend to come and go. That's why we all need to write them down. Even if they're not complete, you can do that later. It's better to write something that you'll change later then to forget it without putting it on paper.
Books, note pad, voice recorder, cell phone, computer, type writer, tablets or toilet paper; what ever you can use to write it down.
Ideas are the mortar that will help you build your wealth. Don't take them lightly.
Come back and revise them. Do this at least once a week. Would be better if you do it once a day. Keep them safe and make copies so they'll be secure. You never know what could come out of them.