One of the best approaches would be to have students read good English literature--something that interests them is better, of course; and afterward they should write up a synopsis or short essay on what they have read. These short essays should then be corrected in detail by the teacher.
Its a lot of work, but I think this is a practical way to help transfer the students' passive understanding or comprehension of the text into a more active expression of the habits of English writing, word choice and grammar.
Basically, I think we learn a language, whether one's first language or another, by participating in the associated practices. Comments on what we read is one such practice --at a higher level.
Strangely (or not), learning English Grammar does not enable you to write properly. Writing and learning Grammar appear to be two different accomplishments, although intuitively they seem related.
I have taught both ESOL and IELTS in the past, and my recommendation is to encourage students to write and re-write the same pieces while the teacher corrects each attempt. While this can be tedious for both teacher and student, it works.
Not even native English speakers can write without mistakes!
You can always be careful about your writing, but even when it is grammatically correct, the context may still be wrong.
Read actively and write down the words/phrases you read that you would like to use yourself. That way you will be sure when you incorporate them into your writing that they are correct.