the oxford comma is a line in a song by Vampire Weekend.... (snark, snark)
I ended up going back to college to take a linguistics class. Please don't ask me what I paid for it, but I needed to be reminded what the parts of a sentence were and catch up once more on the basics to understand my S & W. My problem, once I had all that down, (and yes, this old lady aced it) the class ended--before we reached punctuation! GRRRRR! I'm grammar deficient to the point of insanity. I even hired an editor too teach me proper grammar. She is not responsible for how I misuse her advise.
Bottom line? The linguistics class was a relief. It was so logical and precise and comforting (note the avoidance of the oxford comma debate and alienating readers) that there were truly simple and easy rules out there. The bad news--working with an editor and as I read books--there turns out to be a huge amount of 'art' to grammar. The reason for grammar usage can be an artistic statement and far more important than the 'rules'. Top this off with the simple fact tha,t as you read any book today, you will see many of the rules broken by modern editors with almost complete abandonment. Worse yet? It seems to be by accident or simple lack of grammar knowledge. *sigh*
Now my learning method is to take a book that I KNOW is well written and diagram sentences. I love doing this with Ian Rankin. Nothing beats diagramming sentences. Keep your Suduko; I find diagramming oddly comforting--even though I continue and will always continue to abuse the grammar rules. Of course, many of those well written books I mark up with my pen are written by English authors (Ian Rankin) & they have an entirely different set of rules from those of us on this side of the pond.
I wish you well on your pursuit. There are also tests on line you can access, charts that are wonderful, but when it is pen to paper--they never seem to work for me. Also someone told me to just read it and insert commas where I pause. Excuse me, I am a trained oral interpretation person. I pause before important nouns or verbs--not at inconsequential predicates and phrases. I rarely stop at periods when reading, unless it is important to make sure someone listening is 'really hearing' what I think they should.