Writing has always come naturally to me. Yes, I have occasional typos, but I've always had a knack for the rules (and even the exceptions to those rules). On my college papers, I've only ever written first-drafts, and I get As on all of them. And because it comes so naturally to me, I get extremely irritated when people abuse and misuse grammar, especially since many of the mistakes are rules you've used since childhood. And these irritations even extend to my personal life. If someone texts me using numbers as letter replacements, I will not respond. And with my students, I am harder on grammar than I am on actual content. (In my defense, ideas are easy; execution is not. And that's how I compare the papers.)
They're, Their, There I really don't understand why people still confuse these. They're not forgotten words. In fact, they are probably among the most commonly used words! They're is a contraction. Do people even remember what that means anymore? It combines two words together, and the apostrophe denotes such. Their is possessive. There's no real gimmick to remember this other than it's not they're or there. And as for there... it has the word "here" in it. The two words are so similar, and the only difference is the distance of the object! My CD is here. No, my CD is there. The misuse of these words annoys me more than any of the others. They're words we learned in first grade and learned how to spell in second.
Further/Farther I'm always reminded of the film Finding Forrester. Jamal explains, "Farther is in relation to distance. Further is a definition of degree." Well, that's not so hard. Farther = distance. This one annoys me when supposed intelligent characters on TV or film say further when they should really say farther. In fact, I think most writers put down "further" as a default. (While I'm at it, I also get annoyed by TV and film programs that ignore common sense. Like in High School Musical 2 - I'm not ashamed to admit I've seen it - where girls are singing on a stage without microphones, yet you can hear every single one of them. Or in any medical program where they just stab people in random places with a needle. Doesn't the needle have to go into a vein for the liquid to work?)
A Lot It's two words. To the fifth grade teacher who started this trend: I dislike you. A lot.
Its vs. It's Sigh. As a columnist for my local paper once wrote, you wouldn't put an apostrophe in the middle of Hi's or Her's, so the possessive doesn't take an apostrophe. Or, if that rule is too hard to remember (sigh, which for some people it is), just remember that a contraction brings two words together! It's = It is.
Misspelling Definitely Definately? Is definate a word? No... but DEFINITE is. If something is definite, it is a sure bet, certain, unchanging. Therefore it is finite... and what do you know? Finite is in the word definite. Mind-blowing, I know.