I recommend to all aspiring writers of fantasy and SF that they read primary source. Lots and lots and lots of primary sources. From all over the globe and all through history. It's Good For You.
This isn't to do research. It's to expand your horizons. And knock your block off. To learn things you didn't even know you didn't know. You will read things in which people will casually assume something you never even dreamed that other people could think. It will let you in the possibilities. And you will learn that even if people thought the way you did, they could talk about it, and reason about it, very differently. It lets you get inside the heads of people different from you.
(Be duly warned: everyone writes for a purpose, and therefore you will need to read between the lines all the time. OTOH, reading lots of primary source will help you develop that, too.)
It also develops a sense of how a society fits together. An instinct that alerts you to whether you really can throw together a society from bits of another.
And it gives you bits to throw. Reading primary source for folklore, for instance, is a wonderful way to find new monsters. No matter how demented your imagination is, the chance are that millions of souls working at the matter could come up with something more demented.