A dictionary is important to have handy as you write and read for your class assignments. This version of the Merriam-Webster is easy to use and includes interactive games and quizzes to help improve your vocabulary.
Grammarly is a resource that not only checks for spelling and grammar errors, but also whether words are being used in the wrong context. In addition, it provides individual feedback about common mistakes and how to make improvements.
Grammar Girl provides a plethora of in-depth information about grammar and punctuation in a concise and easy to follow manner. Visitors can also access podcasts and archive issues.
"Successful writing in college and university courses isn’t only a matter of choosing a worthwhile topic and observing grammar and mechanics rules. It requires writers to follow a host of other written discourse conventions."
The Hume Center for Writing and Speaking at Stanford University has paraphrased a paper about undergraduate writing errors and "found that these errors are the most likely to attract readers’ negative attention"