Buy a dictionary and a thesaurus. A dictionary can help you double-check your word usage as you write and a thesaurus can help you find new ways to express your thoughts. A strong vocabulary is essential to better English writing.
Focus on English as your primary language. Try to think in English and speak in English whenever you visit a store or are out in the world. The more you think about English and practice using it, the easier writing will become.
Find a study buddy who is experiencing some of the same difficulties you are and take turns writing short essays for one another. Your buddy can help you if you get stuck in certain areas, and getting together to work on the language will have a positive effect on your writing skills.
Read English books, newspapers, magazines, and any other printed media you can find. Reading English will help you recognize patterns in grammar and spelling rules and will help organize your mind to think in written English.
Use a book on grammar to ensure that your sentence structure is correct. Grammar and punctuation often trip up even native English speakers, so do not feel frustrated if you mess up now and then.
Write as much as you can and as often as you can. The more you write in English, the more your written English will improve. Stay positive and approach the task with your full attention.