Principles:

Capture everything: Do not assume your brain will remember anything. Write it down ASAP. Use whatever will let you capture it quickest, whether that's pen and paper or a digital solution.
Review and process: Make sure you actually look at the things you wrote down regularly and organize it. If it was an idea you need to act on (e.g. a topic for a blog post, or a reminder to look up a particular concept), add it to your task manager. If it was a thought for reference, add it to your 'second brain'/note-taking/archive system, and add tags so you can find it easily later. Once processed, archive or delete the item from your capture system.
“Everything should be made as simple as possible, but no simpler": There is a balance to strike between using as few tools as possible, and using many tools that are each specialized to do one thing really well (a tool that tries to do everything tends to do nothing well).
Consider sustainability: In an ideal world, I would only use open-source, non-proprietary tools. But often commercial tools do a better job and/or have a nicer interface. In these cases, ensure that you can export your data at any time in a standard format (e.g. markdown, xml). Also, be prepared to pay a subscription fee - this helps keep the tool going!

What I use:

For capture: Google Keep. If it's a task, sometimes I add it straight to my task manager (Asana).
Info sources: I use Feedly to subscribe to lots of RSS feeds. When an article comes in that I want to read, I add it to my 'read later' board. I also use the 'Save to Feedly board' Chrome plugin to save any article I find on the web to 'read later'. The goal is to maintain inbox zero in my 'read later' board - I remove an item once it's read, so I know that anything in there is unread/unprocessed. I use Goodreads to manage my books, and Castbox for podcasts. I get free e-books and audiobooks from the library, and I also have an Audible account.
For archive, reference, notes, and high-level planning: Notion. I use it as a personal wiki. It is very flexible, easy-to-use, and has relational databases(!!) If the mobile app was faster it would replace Google Keep as a capture method for me. It could also in theory become a task manager (using the database feature) but it currently lacks some key features (like recurring tasks). FYI, you'll likely need to subscribe to the pro version to get enough space. I think it's worth it.

John Haprian