Hey!!!
So the short answer is, I don't really take notes (although sometimes I do)
With the internet, I don't believe that taking notes from a book is very useful in most cases.

What  you want to develop is _assioicative_ knowledge. For example, you know  that in the book Four Hour Body Tim Ferris talks about how to lose  weight for martial arts competitions, but you don't remember exactly  what he said.

This is perfect!!! You can just Google it. Or  re-read that book. When reading books, you don't want to make your  knowledge deep. You want it to be shallow and spread over everything.  For example, if I wanted to know about the best way to evaluate a  company using their managerial team, I know that this is a chapter in  the intelligent investor. Although I have no idea where, and I don't  remember a part of it!

With the internet, we get this really cool effect where you don't need to know the specifics of anything.

There's  this story of a famous American businessman. People claimed he was the  smartest man in the world, because he was so incredibly rich.

One day, a news reporter goes to debunk this. They ask him:
"How many gallons of Oil does the USA buy every year?"

The  businessman presses a button on his desk. He's connected to an expert  on oil economics in the USA. He answers "1.28 billion a year"

The  newsreporter remarks "calling someone up and asking them the question  clearly doesn't make you the smartest man in the world"

The bussinessman replied:
"No,  what does make me the smartest person in the world is knowing that I  know nothing. Having friends that do know things. And being able to talk  to them to find out the answers of any question I may have"

The  moral of the story is that you don't need to go deep for information in  books. Just like how that businessman had a speed dial of people, we  have the internet. (PS: you bet I got this from a book 😛)

So, read as much as you want, as fast as you can. You don't need to remember it.

Another  thing, books are strange. I've just read Thinking Fast and Slow. I  can't recount any one single experience of the book, but I know the  whole picture. Biases are everywhere and we must know this.

When  you read books, you don't really come away with information, you come  away with experience. The best people in the world who have worked in  that field for 20, 40 years are distilling all the information down so  you can learn it in a few days.

If I'm ever designing a lesson plan for psychology students. I know there's a chapter about it in this book.

When you read, you come away with life experience, life lessons. There's a nice article on this:
https://medium.com/the-polymath-project/its-okay-to-forget-what-you-read-f4ef1c34cc01

Okay,  so when do I take notes? If I'm reading something and I think "hey,  this information is useful to my life right now. I need to remember it,  so I'm going to write it down".

Actually, I don't exactly write  it down. I ignore the page and try to write what I just read. Often  times, I'll forget most of it. This is fine. I'm implementing active  recall here. The same principle is used in flashcards to help you  remember things.

This helps me remember it for longer, and it only takes a couple of seconds so it's worth it :)

I don't try to write everything down.

I have a private blog post on my blog where I write down all the things I read in books. I used to do it in my notes app :)

I prefer digital storage because I can crtl + f to find it on the page, if I remember a part of it.

So, in summary, I:
1.  Don't aim to memorise books at all. I aim to create shallow water that  strecthes out far, because If I need to remember the specifics of  something I can just Google it.
2. When I do find something that is  directly useful to me, I write it down in some digital notebook so I can  find it. When I'm bored, I'll read through it.

I don't use flashcards, because that's a habit and I'm bad at making habits as it is.

If you're using a Kindle, you can use Readwise (paid service, not affiliate).
readwise.io
They  email you daily of some cool Kindle highlights. They also have  flashcards and stuff. I'm not paying for them, they send me some  highlights every couple weeks to try and make me pay.

Although 2 really important tips for generally reading books:
1. Skip the parts you find boring. You don't have to read from A to Z.
2.  Rereading a good book again is 100x more effective than reading a new  book (this plays into memorising things. Once you've read a book a few  times, you'll know a lot about it)

Hope this helps!!! :)