So, let me talk about myself for a second.

When I read fiction, I can blaze through a book in a week or less because I simply read it to the end without thinking about it. I don't give it the English Lit. treatment and analyze it. I do that the second or third time through.

With history books, it can take me weeks or months, especially when its a subject I have never read before. Alison Weirs The War of the Roses honestly took me two or three starts, stops, and restarts before I finally read through it. The first 150 pages were so dense with background and family lineages that I kept getting lost.

With history books, don't zip through them, re-read a page two or three times till you understand what they are talking about, and if you still don't know, read the footnotes or go find another source and read that to familiarize yourself.

Feel free to stop and write in the margins, throw in a book mark and go hit the internet to look up and learn more about that specific topic if it interests you. Hell come here and ask questions about what you just read. With history books, especially ones that deal with long spans or a lot of info, it's like reading Lord of the Rings or A Song of Fire and Ice, the plot is just going to get thicker and more convoluted and if you're lost or confused you're not going to enjoy yourself. When you have numerous generals all with Von's in their name, or are German or French with a French or German sounding name, you can loose track.

When you take a break from reading and come back a day or two later, go back and read the previous page or two for a refresher.

Depends on how long you have to read it and what you are reading it for. For me there are three ways I read books.

The first, I read the introduction/first chapter and then the conclusion/last chapter to get a sense of the arguments the author is making. Then I will read a few chapters and maybe skim some if I am trying to save time. This is a good way to go if you are either trying to save time, or are not totally familiar with the literature. Here the point is to get the real barebones of the argument, nothing too detailed, just enough that if someone asked "what is this book about" you could give them the thesis and maybe some supporting facts.

The second way is just normally cover to cover without any notes. This is what I will do if I am reading something that is either not very academically rigorous (so a "pop" history) or is something I am reading to get an overview, but it does not necessarily relate to my research area. For instance, I usually research the Carolingians, but I picked up a book on the early Byzantines just because its related and I wanted a broader understanding. So I read through it fairly quickly, not really worrying about taking notes since its unlikely I would source from it (it was also more of a pop history than anything super academic).

Finally, the most laborious way I read a book is by taking notes and going cover to cover. Generally I will set up my page to list the page number and then either a direct quote or a paraphrase of something that I think is relevant to the argument or my own research. This way certainly takes the longest but in terms of needing to recall specific information later on, its the best way to go.

If you are not familiar with the literature it might make more sense to read it the way I first outlined, that way you can get a sense of where the book fits into the historiography and where it will go. Generally I like the second two ways if I already have some understanding of the historiography, but when I took a class on WWI the first way was my go-to method. Also having two books on the same subject and comparing them is probably the best way to learn what works best.

It depends whether you are reading for enjoyment or studying. If the former I would just read at a steady pace without a lot of note taking. There is nothing wrong with googling a map, dateline or name if you lose track. As you are new to the topic focus most on the big picture and trying to understand the author's argument. It is easy to get swamped by the details. I jot down things that strike me or sources to follow up later. Remember you are reading for your own enjoyment and benefit so you are entitled to focus on what you like.

For studying, make sure you have a grasp of the chronology and key people first then take copious notes, preferably filed by subject not page or book (eg: keep all your notes on conditions in the trenches in one file.) That way when writing you naturally go by theme not by source.

Personally, I read it firstly as a very interesting novel i.e cover to cover. After the first reading I jot down all the relevant dates and names, memorize and finish up with a second slower reading occasionally pausing to make doubly sure I recall the specific dates and figures(people not numbers).

However if I'm reading a subject outside my course scheme for fun I read it like a novel, I end up having a vague idea.