Is using plain language the law?
The following humorous site, “How to Write Good,” is located on the Plainlanguage.gov page. It lists and breaks severa writing rules. In breaking the rules, they illustrate them. It is an engaging way to learn the rules of English–especially since they always seem to have exceptions.
Note that not all of the rules are really rules anymore. For instance, the one about ending a sentence on a preposition is one we have largely gotten out of. (Get it?)