I recommend reading alot of english books, articles and joining forums involving the english language
Also, go on YouTube and listen to english videos if you want to improve your pronounciation.
But writing vise, you can also find guides, tutorials and stuff like that I guess.
And its okay if you make mistakes and people point that out, don't take it by heart.
So to sum it up, reading books is the best method! You can probably also practice writing. Practice practice practice! Learn something new, then practice. Eventually, its going to come naturally . But lastly, learn it properly. Its important since this language is used Globally. So take your time! You may not suddenly learn it ALL in a month, but atleast you will learn it properly
I hope this kind of helped! (My suggestions might not be that good since I've been exposed with an english speaking environment from a young age, so I don't know whats it like)