If you're referring to "ideas", it's usually nothing more than a phrase in one of my pocket-sized notebooks. When I add these to Google Sheets (usually once a week), I have a column for the idea itself and one for general topics. When I've entered all the ideas from a page in one of these notebooks, I stroke through the page with a green, blue or pink highlighter (whichever I have available).

If you're referring to notes, I make notes, mind maps etc on paper and I keep these together in one place. Once they become drafts, I throw them out. I keep my drafts all together in the same Google Drive folder and the filename is something close to the phrase of my idea. Hope this helps.