Hi /r/askhistorians,
Apologies if this isn't a question on history per se, on the other hand I don't think it goes under the banned "help me with my homework" category either.
I'm an undergraduate in Iranian studies that recently got a job as a tour guide to Iran. This tour is quite exclusive and most of the customers will be older academics, well-educated people, and I'm supposed to be an expert on many aspects of Iran, especially its history. I have studied the history of Iran before and know its outlines quite well, but since our examinations were usually home essays I have not committed a huge amount of facts to my memory. For this tour I need to be able to answer a lot of questions on the spot, and I have about one month and a half to prepare. Do you have any tips on how I should go about learning all of this? Should I just read books from cover to cover as usual or are there any special techniques?
Well, real historians rarely learn anything quickly. I can only learn new things "quickly" because I've spent over a decade studying these things and have a lot of existing knowledge to use to incorporate new knowledge. And we don't "memorize" purposefully — we learn it well enough to just know it, in the same way you don't use flash cards to learn anything else you know really well in your life.
But that aside, I can at least help you with your last question. Academic history books are usually written in a way that allows you to quickly extract the relevant information without reading them cover to cover. Graduate students are taught this in history programs. My approach when trying to quickly assimilate new books is the following:
Figure out if this is going to be the kind of book that is worth reading cover to cover. Some are. These are books that really help you set the framework in place, are fun to read, and have lots of interesting facts that are so interesting that you will remember them without trying (because you're interested in them). If it's one of those books, read it first — because you need to get a good framework in your head if you are going to have success with the next method.
If it's not a good "framework" book, then you are just trying to get the argument out of it. To do this, read the introduction. If it is an academic book it will usually include a big overview, a statement positioning the book within the existing literature (the "lit review"), and a totally boring chapter-by-chapter synopsis. This boring synopsis will let you more or less get the argument from the beginning, and figure out whether there are any chapters you in particular want to read all the way through or not. Then, you read the beginning (intro) and end (conclusion) of each chapter. Then you read the conclusion of the book. Taking notes helps. Again, you want to know what the author thinks each part of the book is doing to prove the argument. You are not engaging with the text on a level where you could hope to argue against the argument, you are just trying to quickly learn it.
The combination of these two approaches is what grad students in history do to prepare for their oral examinations, when they have to read about 3 books a day for a semester. It is pretty grueling but it helps you extract a lot of information very quickly, and get up to speed on a topic.