I've always had trouble with grammar. Plus I'm a lousy speller. Been that way all my life. But now, with spell check on the computer, and so many sites divoted to helping you, I really have no excuse. Along with, of course, my Writer's Digest, their Questions & Quandaries section has been the best part of the whole magazine. I've ripped these pages out and just placed them into a notebook in a plastic sleeve, so that when I can't remember how to use certain words, I can just grab it and flip to the page.
It isn't just how to use a word like which, but other words as well. It can get rather confusing: Lay or lying; it's or its; who or whom; lead, lead or led? And there's all sorts of sound-alike words. Like compliment or complement. If you don't know what to watch for, you can read right through and not even notice such a minor (or major?) error, and I know I've probably done this with certain other words. Aside from the word "which", my all-time favorite: Affect vs. Effect. It stumps me every time, but thanks to Brian A. Klems of Writer's Digest, dummies like me get help when we need it.
I had to go through the entire manuscrip in order to find every "which", to make sure I hadn't miss-used it. This was easy to do, even in a manuscript that is over 300 pages long. I just used my "find & replace" option on the computer. Of course, being careful not to hit the "replace" button, until I checked it, plus, if I did change it, I would still have to illiminate the comma in the sentence, and probably rewrite the sentence. In some cases I could see that I needed to re-write it, or could simply split the sentence into two.
I discovered a new (to me) site called "Grammar Girl" http://grammar.quickanddirtytips.com I found this site where you can read, or listen to explanations of common grammatical conundrums. It is very easy to use, and has all the problem words lined up on about 4 or 5 pages that you can click on which ever one you want--ooo, there's that word again--and it will take you to a separate page for a full explanation and usage.
I liked her "quick and dirty tips" in each section. Mignon Fogarty goes into very detailed usage, hitting anything you might need on the word(s) in question. I placed her site on my desk top. I can't live without it.
With my dyslexia, the find and replace option helps me find words that might have slipped by me several times, not knowing that I'd miss-used or miss-spelled it. Which makes me so darned mad!