I'm doing this post even though I know my readers are not the sorts to ever mix up words and use the wrong form of to/too/two or your/you're, because these things are pet peeves and I have to do something to make myself feel better about them.
I'm not going to go into the differences between the homonyms listed above, because everyone knows them if they just stop to think. But there are a bunch of other words that seem to cause a lot of trouble, and drive me nuts. Here's a partial list, with the correct uses attached.
Roll/role. The former is something you have with dinner, or a means of locomotion. The later is a part in a play, or a part to play. At the moment, my role is that of teacher (properly, role has an accent circumflex--a pointy hat-thing--over the "o" but that's pretty well gone out in English, partly because our keyboards don't have one, at least not without some effort).
Affect/effect. Affect is a verb, meaning to influence (there is a noun form but ignore that. You don't need it unless you are writing literary criticism). Effect is a noun, meaning a result. That which affects me (like bad grammar) has an effect on me (it turns me into a cranky old lady).
Accept/except. The only reason I can see for ever confusing these is that no one bothers to enunciate nowadays. I would love to accept the award, except for the part about being perfect.
Critic/critique. I'm sure this was just a typo where I saw it. The critic (a person) writes the critique (an analysis of the good and bad of something). Critique can also be a verb: when I write my critique, I am critiquing the work. Critic, on the other hand, can never be a verb. The critic remains a force for evil in the writer's universe. I mean, a source of helpful input.
You don't have any trouble with there/their/they're, right?
I will also refer my readers to this wonderful discussion of the non-word "alot." It's not new, but it's wonderful.
Oh, yeah: and you don't form plurals with an apostrophe. Ever. Possessives, yes. Contractions, yes. Plurals, no. And, just to keep you on your toes: the possessive form of "it" is "its" rather than the more logically consistent "it's", which is a contraction of "it is." Got it?
Now, for the more controversial side of what I want to say. If you are a writer, you want to get these and more right every time you write in public. That means that when you post in a forum, or on your blog, or even Tweet (I don't follow Twitter, but if grammar and spelling are ignored there, I'm unlikely ever to start), you look it over before you hit "send" and you fix the spelling, put in the capitals and punctuation, and double-check that you're used the words you really meant to. Because if your posts are poorly written, I'm going to make some assumptions about your book. Maybe that's not fair, but it's the way I am. And I'm not alone.