I end up having to refer back to the actual book

Good! My dirty secret, and I'm sure I speak for other academics, is that we don't retain so much information. Rather, from experience, I'm very good at finding information and knowing what information's important.

Let's take a jump to a different field. When teaching kids to read, there are two theoretical "schools:" sight words and phonics. Phonics emphasizes learning the sounds of letters and morphemes so that one can sound out a word and recognize it. The symbol "cat" is weird and arcane if you're four-years old, but if you know that "c" "a" and "t" represent certain sounds, you can say it aloud and produce something you do recognize, the spoken word "cat." Sight words are words that a reader can recognize instantly and don't exactly "read." "Cat" isn't a series of letters, but a symbol itself that a reader has seen enough times that they can comprehend it without having to sound it out. There's a pendulum of consensus that swings from one pole to the other every so many years as to which is more effective- of course, no one teaches or learns purely in one method. Sight words let you start reading things more quickly, but can't help introduce new words. Phonics lets you pronounce words you've never seen, but is a slow build up.

Now, even the most phonetically taught reader will start picking up sight words and not have to sound them out every time, and a sight-word taught reader will add to their vocabulary perhaps even without knowing how to say the words they've learned. A capable reader, of course, needs both a healthy lexicon of sight words and a competence in phonics. This is why learning new languages can be so hard- in your native language, you have so many sight words that you don't even think about. When all the words are new and you have no sight words to rely on, it's incredibly intimidating. There's no way you've consciously thought about all the "the's" and "you's" and "so's" I've written. Sed dum aliā linguā scribo, lente legere debes.

This is why when I teach any language, the first lessons are on how to read an entry in the textbook's glossary, a typical dictionary, and on Wiktionary. I've found that as much as students are hesitant, or even scared, to try anything in a new language when they've had three weeks of classes, they can be surprisingly bad at using those resources. My most common phrase in the first weeks of class is "Did you look it up?" If you're not sure what you'll find in a glossary, it's a lot easier and less risky to ask for help, or to just give up. I try (emphasis on try) to communicate that it's absolutely okay to not know things.

One way to do so is clearly differentiate what we call "formative" and "cumulative" assessments. Formative assessments ask how you're coming along with what we're learning- it's okay to not know things here. This can be proper quizzes, or it can just be daily math problems or in-class speaking exercises. Cumulative assessments are exams or essays- these are goals that students should work towards. They also serve as benchmarks: "If you don't know these things by know, you will have a hard time in the next part."

It's important to distinguish what will be on that cumulative portion, and to make what's on it important. Students know that learning "videocassatera" means "VHS player" is a waste of time, and pretending that they have to for any other reason than that it's in the textbook is silly. There's vocabulary and facts and dates, and then there's the important stuff. In a language class, that will be those "sight words" or equivalent grammatical structures, i.e. the things that if you're looking up every time will cause you huge trouble. It's my job as an expert to identify what those things are, because I have the experience to be able to.

What does this have to do with anything? This is a little bit of the thought process of a teacher. If you're your own teacher, you should:

1. Pick out the important stuff and set goals. What do want to learn? If you were taking a final exam, what questions would you be proud to know the answers to? What things keep coming up in your readings? Those are these things you should aim to know, and will make you a better scholar if you can recognize them when they inevitably come up again. Academic writing is based in case studies- identify what facts are specific to the case studies (e.g. place names on one island in one battle in WWII Pacific Campaign or characteristics of a regional pottery style at a neolithic site). Those are nice to know, but don't waste your time taking notes on that. For more, see /u/sunagainstgold on How to Read an Academic Book

2. It's okay to now know things. You're just starting. Do not feel bad about looking things up- in fact, get really good at. Get comfortable with indices and appendices. Get to know tables of contents and abstracts on library websites. Rather than trying to organize notes, organize your books and ideas. I use Zotero to organize readings; I make sure they have abstracts or tags to remind me what info is in them. A lot of my friends use the Zettelkasten Method for notes. Instead of writing down notes for each book, you write down ideas and thoughts and concepts that come up in them. If you're reading about US government history, you might end up with a notecard that lists overturned Supreme Court decisions. When you come across that in a reading, you note it on that card along with the citation, and on other related cards as well: "Devolution of Power" or "President-Court conflcits" or "Times the Court Decide it Shouldn't Be Racist Anymore." This helps you to find things again, to make connections between readings (which helps remember them), and to fuel novel insights. Don't just write down info from the books. It's already in the book.

3. Recognize that you will get better with time and you won't remember things right now. Don't give up- but don't expect too much from yourself. This is your formative stage and you're relying on phonics and a couple sight words. It's not the cumulative evaluation, and it shouldn't be. Me not knowing much was a white lie- I do obviously know more off the top of my head on my subjects than all but a handful of people. But I didn't learn that from reading- I learned it from rereading and from using it. I know dates and names and places because I've written those things for AskHistorians answers, for term papers, and for conference presentations. I also know them because they keep coming up. As mentioned, those are things that are important to know, but those are also things you might not have to put much effort into. It takes time.

You are not stupid. Einstein said he had no special talent, he was just passionately curious. I believe that people are "stupid" not because of a lack of ability, but a lack of motivation and curiosity, and you've clearly shown an abundance of that.

I would say the best learning technique is the one that's sustainable, the one you enjoy. Try to relax and not get discouraged. History is infinitely complex and not being able remember every detail immediately does not reflect badly on your intelligence.

It really depends on what your goals are. Revising a specific thing for an exam? Write notes. General learning for fun? If you don't enjoy note taking, I wouldn't recommend it.

I think the best way to retain information is to be able to contextualise it. If you have a broad overview of the historical narrative, it becomes easier to place specific events within it, and how one thing influences another. So personally I wouldn't worry about getting all the details down at first go, but rather read for the big view, and fill in the rest later. This comes to another point: repetition. You can't study British history without encountering some French history in their and vice versa, after time the facts will be absorbed and you'll be able to appreciate them from different perspectives.

I also sometimes ask myself to revise something I learned. For example I imagine someone asking me to explain the history of Germany from pre history to the modern day. When I come across gaps in my knowledge, I make a mental note to look into it later. Putting things in your own words is very valuable in the learning process. In contrast to note taking, it's a creative process and challenges you to synthesize your knowledge in a way that makes sense for you. Also, rather than trawling history for everything, it helps to have specific questions in mind. A question that interests you and is fun to answer. You can focus on the details that address that question and when you come back later with another question, you'll already have some familiarity to build on.

Everyone is different and I've known people that find techniques like neumonic devices helpful. Experiment with what works for best for you. Focus on improving your own knowledge rather than comparing yourself to an imagined person who's so much better than you at learning history. I hope that helps!

Well what I try to do is to see everything as a flow because history is really a flow of events. Plant everything on an imaginary timeline in your mind and that should help! Many events occur either simultaneously or as a "cause-and-effect". Hence, if you can see the connection, it should be much easier.

Or you could try actually picturing historical events. So I had to prepare for an exam on the UN and it included its efforts (or the lack of) during the Rwandan Genocide and what I did was to watch the movie "Hotel Rwanda" which sort of gave me the context on what was happening them and now, instead of memorizing the specific details from my notes, I can visualize what happened through the movie. BUT this depends on how factually correct they are as well so perhaps you may have to create your own visualization :)

Hope this helps!