Could you mention your current speaking level, since both speaking and writing are productive skills. Also, both reading and listening are receptive skills. Your productive skills need much practice, reading for writing, and listening for speaking. Actually, writing skills are so important in formal English, and for your study/work. You need a systematic approach to improve your writing. Firstly, read more and more several material, and preferably the materials which you are interested in. Secondly, try to summarize every essay, or paragraph you just read. Thirdly, Pick up the important vocabulary to keep in mind. Finally, write an essay for every day using the correct structure, and a different topic for each essay. Hopefully, this technique helps you with your purpose.