For over twenty years, the simple, friendly approach of THE LEAST YOU SHOULD KNOW ABOUT ENGLISH has helped students with their spelling, punctuation, and sentence and paragraph structure.
The Least You Should Know About English by Paige Wilson (Heinle & Heinle Publishers 2005)(428 +/-). This was used as a textbook for remedial freshman English in 1979 in my small liberal arts college. It remains the most useful guide to the proper use of the English language that I have ever stumbled upon. I cannot recommend this volume highly enough to do it justice. My rating: 9/10, finished 1979.