Of all the errors that Shaughessy covers in Errors and Expectations, spelling and vocabulary are two that are most clearly connected to reading. Spelling isn't completely random in English, but there are too many rules to simply memorize, even with the drills that Shaughnessy provides (178, 180). Exposing students to one rule that would significantly improve their writing sounds like a good idea. That way they don't feel like there's simply no way to learn to spell. But on the other hand, bombarding them with lists of rules had got to be more intimidating that handing them a dictionary and teaching them to use it. It's good to help students realize that there's a method to much of English spelling's madness. But let's not fool ourselves--spelling is mostly memorized and the rules that Shaughnessy shares are probably best learned simply by internalizing the patterns through reading, not through drills.
I think Shaughnessy's approach to vocabulary is more workable. She admits that real gains in vocabulary are subject-based and take time--exposure to the vocabulary of the field (224). It doesn't hurt to learn word parts--unlike spelling, which is usually memorized or guessed at, word meaning really can be deciphered by taking a word apart and looking at the meanings of its parts. Again I'd be careful not to overload students with charts or drills, but studying a few basic roots and prefixes and exercises in explaining the shades of meaning among synonyms really shoud help students have an easier time with words.
Shaughnessy, Mina P. Errors and Expectations: A Guide for the Teacher of Basic Writing. New York: Oxford UP, 1977.