The single best, surest method
Find a fiction book in modern English. Not a textbook, not olde English (like Shakespeare or Pride and Prejudice even). Read a few pages; if you cannot understand many words, select an easier book. Missing 5 words or so on a page is ok. Is this book interesting to you? If yes, buy that book. If not, find one that meets my criteria that you are interested in.
Read that book, every night, for 15 minutes. Every night, not just sometimes. Preferably last thing you do before sleep.
Read for the story, for the flow, for the feelings. Do not treat this as a grammar or learning exercise. Do not stop to lookup words you don't know. This is vital. While doing your reading, guess the meaning as best you can from the context. By all means, look the words up tomorrow, but while doing your nighttime reading, guess the meaning and keep going.
Your job is to enjoy the story as best you can; allow your imagination to bring the story to life for you.
While your conscious mind is engaged in enjoying the story (if you have followed my advice and picked according to my criteria), you are distracted from telling yourself, "I'm terrible at English. This is too hard for me. I'll never learn those grammar rules" and so on. Instead, your conscious mind is enjoying itself, "seeing" the story unfold in your mind, causing your emotions to respond.
Meanwhile, your tireless subconscious is observing. It is matching sentence patterns with imagery, with emotional responses. Building associations between ideas. Noting sentence structure, empirically deducing grammar rules, absorbing vocabulary and the different colors of meaning of familiar words.
When you fall asleep, all of this is fresh on your mind, and your subconscious, which doesn't sleep, goes to work building the physical memories and structures that allow us to draw memories, form sentences, choose the best words for a given feeling, etc.
You will literally do most of the heavy learning while you sleep. This is a time-tested method for acquiring language. It is by far the best effort-to-reward ratio of any technique for learning language.
It would be an extra bonus if you have access to a native speaker willing to discuss the book with you. This is the extra step that puts all that you have learned into active use.
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