Reading your first novel in a foreign language can be a pretty disheartening experience. Staying motivated is obviously key, but looking up three words of obscure vocabulary per paragraph is no fun.
Here's three reasons why nonfiction books can make language learning so much more enjoyable:
#1: The language in most nonfiction books is easier than novels.
Nonfiction authors know that their readers are looking for information, so they don't tend to hide facts behind flowery language, or cryptic metaphors. This means that apart from a certain number of domain-specific words, the language used tends to be simpler, and the writing clearer.
#2: Sticking to a single domain will raise your comprehension much faster than reading novels.
Any nonfiction book will naturally contain a quantity of domain-specific words that you'll have to learn, but this vocabulary is very likely to be repeated throughout the book.
Not only that, but if you stick to a strategy of mastering one domain at a time there will be a large overlap in the next book you read on the same topic, and even more in the one after that. 300 words and phrases related to environmental issues will make reading the next book on environmentalism so much easier. Whereas reading a novel by Camus doesn't necessarily make it all that much easier to read one by Sartre.
#3: There's likely to be a lot more media out there that you can take advantage of now that you've learned that domain-specific vocabulary.
If you've read a few books on a topic and learned the necessary vocab, you can probably now start watching documentaries and YouTube videos on the same subject with a very high level of comprehension, which makes learning a lot more fun.
Good luck with your reading and language learning, and let me know your tips. Thanks for reading.