It depends on many aspects:
1) common level of your intelligence and education
2) extended or now vocabulary in your own language and the lenguage you study
3) knowlenge of grammar and rules of writing in the language you learn
I can say from my own experience that first it's necessary to understand the goal of a writing.
Then I write down all the thoughts I have about it (but not in detaild). The next stage- to create a plan of writing. Each style of writing requires folowing its specificits (vocabulary and grammar), its own laws of composition. Write a few drafts and then choose the best one to work at. Use online resources to correct grammar. Choose the topics for writing (don;t write about the same things all the time). Find a friend who will read and express his/her opinion about your writings and correct mistakes. The more you write the better will be a result.