Writing requires reading.
That's it, the greatest writers are great readers in the first place! Reading is a skill as well as writing, so it is necessary to develop your skills in reading and there is no better way to do that than practice. The type of reading you should target depends upon your knowledge of language. For example if you are beginner in English, you need to start reading simple and short texts, mainly short stories; short stories usually use a simple language, but it does not main at all that they are less valuable than other types of texts. I still remember that a professor of Literature at Ibn Zohr University told us that short stories are the hardest type of literary texts, because the writer has to tell many things only in few pages. However, short stories are the best type of texts to start developing your reading skills. Moreover, it is not just about reading, but paying attention and reading between the lines.Find a unique topic.
I used, and I am still sometimes, to write about different topics in one text! Imagine you are writing about a general topic, you are likely to combine many terms from different fields. This is going to make the reader confused even if you understand what you are talking about; though I doubt that you know what you mean! In order to avoid such mistake, your text should only be about one topic which in its turn has to be more specific and narrower.Respect the structure of writing.
In English at least, the good writing has to respect rules in term of form and structure. A text, whether it is an article, essay or even a complete book, has to be systematic. It mains that there are steps from the beginning to the end, and there is a structure. To make it more clear, your text should have an introduction, a body and a conclusion. Each of these has its fondamental role. For instance, the introduction serves to present your topic generally and what it is about. It hooks the attention of the reader and tries to persuade him/her. The body is composed of many paragraphs that should be well structured. A paragraph has to have a topic sentence, supporting details, and conclusion. Then comes the conclusion where you conclude the topic. So it is not just about arranging words together and filling in the paper(s), but rather there is a structure. It's just like building a house, you need to follow some kind of organizing.Then practice, practice, and practice ! This is what I am doing actually, I express my ideas and at the same time I practice writing. Thanks for reading.