Story tools has a collection of tools to analyze your writing. For example, you can paste your essay here and check "readability" (it analyzes your sentences (long/short), use of passives, articles, verbs, etc) or clichés, word count, etc.
It also works well to help you create your own stories (use the "story idea generator" button).
Why don't you try using some of these tools before handing in your writing to your teacher? :)
Site with grammar explanations and practice exercises. Great for advanced and C1 learners who would like to review the use of adverbials, verb phrases, etc.
Watch instructional lessons and short clips that will help you learn how to use apostrophes, irregular verbs, possessive adjectives, simple present tense, capital letters, words with similar meanings and much more. Learn online and have fun improving your English language skills.