Follow my rules.

Why the befuddlement over grammar? I concede that the rules shy away from being steadfast and have exceptions, but that does not warrant the blunders that abound in written English. For this fact, here are my (candid) thoughts on the most common missteps:

Apostrophes:
1) Signifying plurals: DO NOT USE AN APOSTROPHE TO SIGNIFY A PLURAL. Example: never say "These pickle's are really tasty." This just makes me want to ask you what the pickles own that are so tasty. The one exception to this rule I will accept is using an apostrophe to separate the digital portion of a decade from the "s" at the end. Example: "Excuse me sir, but were you alive during the 70's?" This prevents (though is not necessary due to contextual clues) one from assuming that the pronunciation is "seven zero ess," as in the specific part number for some gadget. I accept this exception only because English is an absurd language.
2) Signifying possessives: Pronouns (her, it, his, etc.) do not use apostrophes. You would never say "That book is her's." Nouns (dog, cat, asparagus) use apostrophes; "This is Michael's mounted deer head," or "That is the dog's bone." Those are appropriate uses of apostrophes to signify ownership. "It's" means it is, while "Its" means that "it" owns the object of the sentence.
3) Plural Possessives: This one is pretty simple, once you know the rule. With the exception of pronouns, which we've already been over, there is only one way (that I know of) to signify plural possessives. Instead of the apostrophe being between the subject and the "s," simply put it at the end of the whole word. Example: a bowl belonging to one dog is "The dog's bowl," whereas a bowl belonging to multiple dogs is "The dogs' bowl." You don't say "theirs'" however, because apostrophes aren't used to signify ownership with pronouns.

Their, There, They're/Your, You're:
1) They're not interchangeable. Deal with it.

I, Me, Him, He:
1) Mine vs. My in conjunction with a second-person pronoun: this is a rule that there is almost universal confusion over. How do I say that the book belongs to both my brother and me? Or is it my brother and I? The answer is extremely simple once we break down the sentence and put it back together piece by piece. First off, would you say that it is "My book" or "Mine book"? Obviously the first of these options is correct, so now we move on to the second-person pronoun. The only logical choice is that it is "His book", thus the second part of the sentence practically writes itself. Putting the two sections together, we get "It is his and my book." It may not sound perfect and pretty-smooth, but it's right. Alternately, if we want to put the book in the first part of the sentence, we would say "The book is mine and his" because if the first-person was the only object in the sentence, we would say "The book is mine." It's all about treating each pronoun as though it's in the sentence alone, then putting the two together to form one cohesive sentence.
2) I vs. Me: The same process from the possessive sentences we just went over applies to this idea. Most people I've encountered have been poorly taught to believe that whenever you are talking about yourself and another using pronouns, the personal pronoun must always be "I." If we break down a few sentences using the same process for the possessives, however, we see that this is not necessarily a hard and fast rule. For example, if I want to say that I went to Subway, and so did my roommate, I would say "She and I went to Subway" because separately the two sentences would be "She went to Subway" and "I went to Subway." But if I want to say my mother gave a gift to both my brother and me, I would say "My mother gave a gift to him and me" because separately the two sentences would be "My mother gave a gift to him" and "My mother gave a gift to me."

Hence:
Oh my Lord few things irritate me more that the misuse of the word "hence." Hence takes the place of "consequentially..." not "that is." Don't ever let me hear you saying "I ran out of milk, hence why I went to Wal Mart." I will hate you. "I ran out of milk, hence I went to Wal Mart," or "I ran out of milk, hence my trip to Wal Mart" are appropriate. It's a vaguely ruled word that is nearly impossible to explain to someone who doesn't understand it. If you don't get it, don't use it. It's easier to respect a person who knows their vocabulary and doesn't try to over step its bounds than it is to respect a person who picks up on words from another's vocabulary without fully grasping the meaning and proper usage.

Can anyone explain the "who" vs. "whom" rule to me? I knew for about 3 months my senior year of high school, but it completely escapes me now.

Also, I couldn't decide where to put the period after a single word in quotation marks, so I just put it within. It looks better to have the period outside the quotations in these instances, but I either never learned the corresponding rule or have forgotten it.

More to come later; I'm all grammared out. (a rant on semicolons, perhaps?)