I'm a Bit Older Than Seventh Grade

I've been toying with creating languages for my own RPG and fiction writing, but never knew how deeply and completely the subject went. So much of what I hear you discuss goes way beyond what I ever encountered in undergrad English classes. Is there or are there any books that you would recommend to someone who is needing a both a refreshing on general English grammar and especially advanced grammar? For then exploring constructed languages, I appreciate any suggestions.