How can one improve their English writing skills and make their fiction more interesting and engaging for readers?

Hi, these are, and should be, two or three different questions. So, let’s do three questions.

How can one improve their English skills?: As with most languages, practice and immersion into “good” English works. This means reading, talking, studying, and practicing. I might suggest studying slang and common speech separately. Definitely study them, but separate from solid, standard academic English.

How can one improve their writing skills?: Like playing a musical instrument, or playing a sport, practice, practice, practice. I strongly recommend schooling, but also read books about it, write every day (do not skip that part, write every single day) and allow this to take time, allow the time, it is much like playing an instrument.

How can one make their fiction more interesting and engaging?: Read a lot—read every day, and read things that you find engaging. Also, read things that you are enthusiastic about. Find some fiction that you love, and then not just love, but find fiction that keeps you up at night. Try to find books that make you want to rush home to read. THEN—try to write like that. Good Luck.