Hi Quarttt,
I started learning how to write with three books:
1. A style manual for reference (preferably one with exercises)
2. an introductory essay reader that includes essay questions and writing exercises
and 3. magazines such as The Economist, New Yorker, and Harper's
This is what I did. Every week, I read a section of the style manual and the essay reader, did the grammar and writing exercises, then worked on an essay. Then I got feedback from an experienced writing teacher, clarified what I didn't understand with him/her, and read a few magazine articles. Reading magazine articles helped reinforce what good writing styles looked like. Of course, if I came across a great essay, I'd try to write one similar in style.
Then I'd start the process all over again, learning and relearning everything until I got it (I know I get it when I know a particular skill so well I can use it without consciously thinking about it).
Hope that helps.