If you want to test your knowledge of commonly confused words, sentence structure problems, and punctuation, visit Effective Writing Practices Tutorial, courtesy of Northern Illinois University. You will have numerous opportunities to take automatically graded quizzes that challenge your command of a broad range of writing-related issues.
This post is the fourth in a row that features a university writing center. That fact alone might keep away people who consider themselves serious business or technical writers. They would be mistaken. In fact, they might be hard-pressed to ace all the quizzes. Try them and see if they help. These exercises for writers are no different from a professional athlete's warmup or a musician's playing scales. Practice!