"...I write good grammar myself....That is to say, [my] grammar is of a high order, though not at the top. Nobody’s is. Perfect grammar—persistent, continuous, sustained—is the fourth dimension, so to speak: many have sought it, but none has found it.... I know grammar by ear only, not by note, not by the rules. A generation ago I knew the rules—knew them by heart, word for word, though not their meanings—and I still know one of them: the one which says—which says—but never mind, it will come back to me presently."
Twain, Mark, Autobiography of Mark Twain, Volume 1, Berkeley, CA: University of California, 2010, Web. 30 Aug. 2013.
<http://www.marktwainproject.org/xtf/view?docId=works/MTDP10362.xml;chunk.id=d1e3698;toc.depth=1;toc.id=;citations=;;brand=mtp#X>

Mark Twain is of course making a joke here. And that is the way that I think we can best enjoy the grammar and its tricks and rules. It is a game that is to be played and enjoyed--with rules followed and even broken sometimes to create ideas that you want to express.

Online resources for grammar:

Purdue Online Writing Lab
http://owl.english.purdue.edu/owl/section/1/5/


UCLA Graduate Writing Center
Grammar Materials