Writing can be the most challenging skill to master in English. Both writing and speaking are what we call productive skills. This means they take longer to acquire than receptive skills: listening and reading. Before you attempt to write in English you should be comfortable at listening and reading, which brings me to my first point - read, as much as you can.
Reading is preparing yourself for writing. Whether you like reading or not, you should try to read for fun every day. You don’t need to read long books to start with, reading news, Facebook posts, Instagram captions can be a good starting point. As you get more comfortable with English and your level improves, move on to longer reading. Start with a short story or a book you already know in your first language. This time make sure you note useful words and expressions you come across. It’s important not to translate but to understand their meaning. Write a couple of sentences to start with using the new words and expressions you have acquired from reading.
Keep a notebook with words you learn while you read. Don’t only write them but practice them. The trick is, don’t try to learn too many at one time. Choose a few words or expressions and write sentences with them. When you add more, always go back to revise what you have already learnt. Once you have a nice amount of these key phrases, try to use them more and more. Write sentences using them.
Start small - write 2-3 sentences a day and gradually increase. What to write about? Anything! You can write about what you did that day, how you felt, what you cooked, who you met up with... Once you start, you should notice that you begin to think in English, which is what you should aim for. Keep a diary for as long as you can, if you struggle to write every day, try to write every week. Set yourself a time when you can focus. After a few weeks or months read your first sentences - did you improve?
Checking your work is very important and will help you eliminate many mistakes. Many English students forget to read their own work. It is very common and it is not a good habit. The most effective is to read your own writing after some time. I recommend leaving it for a day and reading it again. Try this technique and let me know if it works for you.
You should practice as much as you can in order to improve. Set yourself a realistic goal - do you have enough time to practice every day? Can you write every week? It’s important to do it regularly at a time convenient to you. So, here is how to start improving your writing - get reading, note phrases, start writing and check your work. The more you do it, the better you become. Good luck!