Read what you love (and why the right level is still important)
Please note that I write about my own experiences and thoughts. I describe what works for me and what I enjoy. Some things work well for many people, but not everything works for everyone. If something else works better for you, that's fine! I just want to share my experiences.)
Some time ago, I read the following advice:
"Don't care about the right level, read what you love!"
It's funny, because this is what I did before I switched to my current way of reading and although I tried to read articles about topics I'm very interested in I was very frustrated because I needed to look up almost every word (which is no surprise since one of my favorite topics are history and science XD).
It was no fun at all and I didn't made any noticeable progress for months. Maybe it's because the books and topics I really love are much more difficult than the books other people love (certain mangas or light novels, for example).
Does the level matter or not?
This advice is not bad, but it really depends! Even if you love certain topics or series and if you are very motivated to read it in your target language, this is not a guarantee that you will really enjoy it. If it's too difficult to follow the story there's not much to enjoy. At least, this is what I experienced.
In my case, choosing reading material that is around my level or not too far above was the best decision ever. I made so much more progress since. I don't follow a certain rule, like, "read material you understand to X%" or "read material where you understand X of 10 words".
I'm also really bad at guessing the level of difficulty in general. I'm not familiar with the JLPT levels. I can only describe how easy, normal or difficult it is for me at my current level. When I describe the level of difficulty it's very subjective.
This is how I describe easy, normal or difficult books:
Easy: 『ペンギン・ハイウェイ』 was the easiest novel I've read so far. I looked up a few words, I didn't understand every detail but I was able to read it comfortably. I understood most of it.
Normal: 『ぼくらの7日間戦争』 was normal. I didn't understand everything and some sentences and paragraphs were difficult, but overall I was able to follow the story well enough to enjoy it.
Difficult: The 『ハイキュー!! 』 novels are difficult at the moment. The story is not complicated but the author used a rich vocabulary to decribe even the simplest things. I'm used to not understanding every detail, but this writing style made it difficult for me to understand what is going on. I really love 『ハイキュー!! 』 and I will definitely come back to these novels, but I will expand my vocabulary by reading books that are easier to understand, before I try it again.
I recommend to read the excerpt of a certain book (if available) and see for yourself if this book is at the right level for you.
I always try to read the first chapter or two to tell if I understand enough to enjoy the book. I follow my gut feeling, not strict rules. The right level is a level at where I can enjoy a book. So in that sense, level does matter in my opinion.
If your favorite books are too difficult at the moment, try to find books at your level. Easier books can be interesting, too. Maybe you'll find your next favorite book.
Let's say you want to read this one light novel series in Japanese, because you enjoyed the anime in your native language (means, you are sure that you will love the light novel, story-wise).
But when you only understand fragments (a few words or sentences here and there) so that it's very difficult to follow the story, it might not be so enjoyable as you thought. You won't get much out of the book at this stage. At least, this is how I feel.
Instead of forcing yourself to read something you "should" enjoy but which is too difficult at the moment, I think it may be a good idea to try something else for now. If your favorite light novel or manga series is too difficult at this stage, don't hesitate to try something new and broaden your horizon — you may discover your next favorite book, who knows?
It's not a shame to admit that some books you are interested in are too difficult at the moment. If you are open minded and curious and also try books other than the popular manga and light novels you already know, you may discover even more books that are interesting.
I've read books which seemed not so interesting in the beginning, but in the end I was so glad that I've read them. Don't judge a book by it's cover!
The most important thing for me is to keep going. Books I barely understand only slow me down. That's why I rather try something new at the right level instead of insisting on that one cool series which is far above my current level. I learned so much by reading books that are around my level and I enjoy this process much more than before!
When I choose a book, the content is not the only important factor. The better I understand a book the more I can enjoy the content. It is very motivating if you read a book in your target language and realize that you can follow the story without too much trouble. This can give a language learner a lot of confidence! There may be countless books you can't understand, yet, but it is a great feeling when you read something you can understand well (enough).
Mixing the level of difficulty
As I wrote above, reading books which are not too difficult are very important in my opinion. However, in order to improve I don't avoid difficult texts completely. I'm experimenting with reading books at different levels. Reading something difficult is hard but challenging yourself is beneficial:
Difficult texts are not scary anymore
If you are mixing different levels of difficulty you'll get used to reading difficult texts. It's still difficult, of course, but you won't develop the habit of only reading easy texts and avoiding everything that is more difficult than what you are used to. You'll gain confidence with every challenge.
In my experience, the first few chapters of a new book are usually the hardest. After you are used to the story and writing style it often gets easier. If you are used to difficult texts you won't give up on the first few pages.
A more realistic feeling for your real level
Reading only things at exactly your level can lead to the impression that your language skills are at a higher level than they really are. If you read things at different levels of difficulty you'll get a more realistic feeling for your current level. You'll learn in which areas you need to improve. Are you lacking vocabulary? Or is grammar your weak point? If you know where you stand you can choose your language learning activities accordingly.
Keep learning something new
Leaving your comfort zone regularly makes sure that your progress won't stagnate. At some point, some texts are so easy that you won't learn much from them. It's absolutely fine to read easy books, of course, but I think it's a good idea to mix them with a bit more difficult books so that you'll keep learning new things.
My main focus is on easy/normal books, but I also regularly challenge myself by reading at least a few pages of a more difficult book. I'm mixing extensive and intensive reading, so to speak. This way I don't get overwhelmed by the difficult book, where I need to look up much more words to understand what's going on.
If there's an interesting but difficult book you can't wait to read, this strategy may be a good compromise.
