A pen and a notebook have been a great productivity tool for me. I take notes and ToDos. I write down deadlines and important dates. When a ToDo item is Done, I strike it off, so as to keep track of what is pending. For taking notes, I prefer to use a spiral sketchbook that is turned over by the side rather than a notepad that is turned over at the top. Why note taking has been a crucial skill for me as a tester. I take notes,

• About an application under test
• During requirement discussions
• During testing, making notes of issues
• For test idea generation
• To keep track of the queries
• To keep track of the issues
• To keep track of the deliverables, deadlines and it’s status
• To remember important points during calls and conferences
• To note down ideas or suggestions …etc.

The benefits of note taking:

• “Note taking isn’t just about recording information. Effective note taking is thinking on paper.” – Nicole Liem Yang of Show Me the Notes
• Not only do good notes help us recall facts and ideas, there’s good evidence that the act of writing things down helps many of us to remember them better.
• By jotting down what you need to remember later, you can then turn your focus on what you’re hearing or reading. You will have room to ask follow up questions or clarifications
• Notes help us to prioritize the important. 
• Notes help to eliminate the communication gap.

We have smartphones and laptops. Then why use notebooks?

• You have a significantly higher chance of achieving your goals if you write them down. This is likely why vision boards or lean visual controls have become popular. 
• We can always have that handy and in sight, thus reminding us of our priorities.

A few tips on note taking:

• Keep it short. Yet, it should be clear so that you understand when you refer to it next time.
• Don’t write down every single word.
• Focus on important points.
• Use abbreviations or short-hand writing.
• Forget spelling and grammar.

Here are a few note taking methods

• Cornell Style of Note Taking
• The Outlining Method
• Mind Mapping

One of the greatest note-takers was Leonardo Da Vinci, whose notes (Codex Leicester) were bought by Bill Gates for over $30 million and are exhibited today to the public.

References: 

https://en.wikipedia.org/wiki/Note-taking

The Importance of Note Taking to Being Successful

Note-taking as a Skill for Testers

https://www.lifehack.org/articles/featured/writing-and-remembering-why-we-remember-what-we-write.html

https://www.lifehack.org/articles/featured/advice-for-students-taking-notes-that-work.html

Lean Visual Management Tools: 5 Types of Visual Controls