I’ve created a self-study program to better learn grammar and sentence diagramming. One of my tutorials was the Get Smart Grammar Program from the Grammar Revolution Website. I have now completed all 37 lessons, and I am much better at diagramming sentences.
Elizabeth O’Brien is quite good at simplifying and explaining things. If you are looking for more grammar skilz, including the waning art of diagramming sentences, check out her website. There are a lot of free resources.