I don't know about websites but maybe reading? I actually like doing things like reading the Wikipedia glossary of grammar terms to help me, but I'm one of those weirdos who used to read the dictionary when I was a kid, your mileage may vary.
I appreciate creative uses of language but do have a real sticking point when it seems to me like someone is just totally disregarding it; one needs knowledge of rules to effectively break them.
I've worked hard to improve the lucidity of both my written and spoken language to more effectively communicate things which are important to me and that I want to relate to others in the most effective way possible, while retaining some semblance of credibility. Maybe I've had limited success, I like to think so, but only someone else who can pick up what I'm laying down could tell me. I guess practice, practice, practice is the advice I'd offer to you, in lieu of a website?
I can't say I learned much in school either, until I finally went to college at 42. The rote memorization offered in my secondary education is not how I learn, combined with an utter lack of desire to attend school so that need not be a stopping point for you.
I appreciate your wanting to improve your grammar and language skills, that is commendable and probably hard to do, I wish I had better advice for you.
What about school?
Sine experientia nihil sufficienter sciri potest -Roger Bacon
*γνῶθι σεαυτόν*