Still my writing English is at the speed far short of a desirable level. And still grammatically questionable. Also the wording can be very much incorrect, I assume.

Then, what are the necessary things for my learning English?

First, I need to read through at least one or two grammar books. – Now I made the noun "book" plural, but is this grammatically correct? Even this I don't know. My checking of grammar is usually by googling a phrase, that is, by using Google as a corpus. It is not a solid way of checking grammar, though useful.

By the way, I often try a Google translation for checking, too. Of course, the machine translation is not perfect, but it may reveal syntactical disorder in the sentence in a glanceable way since it is shown in my native language.

Second, I need to read English text more and more. Probably for now I have to make this my routine.

Third, I need output practice – like this writing a blog.

The most fundamental of these is reading. If there is a litmus of one's potential aptitude for English, those three must be considered. If these acts are painful, it may signal a weak potential aptitude. Desirably, if there is no pain in doing such things, it must be a signal of a great potential aptitude for English.