Read, read, read! This is my primary guideline for improvement of the English skills. I'm probably now somewhere in the middle-level of learning English. Currently my WPM (words per minute) in reading is around 150.

But how should I read at this stage of learning? Probably so-called extensive reading ("tadoku" in Japanese) is desirable. But in what way of extensive reading should I do it?

Probably it is this: to not aim perfect understanding of text. At this stage of learning English, a shower of English sentences is what's needed above all. I should look up dictionaries, but only sometimes when I feel like I want to. For a lot of looking up dictionaries may make me tired. Digesting a lot of English text is important at this stage of learning. I have to bear in mind that improvement of the English skills takes time. Perfectionism is harmful at least at this step of learning.