Of all the rules in the English language, the battle between "who vs. whom" is the one I dislike the most. These two words are so similar, and normally I would just fall back on who, hoping no one would call me out or notice. Well, it's time to put an end to that!
After a quick Google search, I found this interesting excerpt at Dictionary.com:
When should I use whom instead of who?
Use who when a nominative pronoun is appropriate, and whom when an objective pronoun is appropriate. Who is a nominative pronoun (meaning it acts as a subject) and is used: 1) as the subject of a verb, as in "It was Paul who rescued the dog."; 2) as the complement of a linking verb, as in "They know who you are." Whom is an objective pronoun (meaning it serves as an object) and is used: 1) as the object of a verb, as in "Whom did you see?" and 2) as the object of a preposition, as in "That is the group to whom the credit belongs." Who and whom seem to cause more difficulty than other pronouns. Thus, when in doubt, substitute him and see if that sounds right. If him is OK, then whom is OK. For example: "You talked to whom? You talked to him." It would be incorrect to say "You talked to he," and few native English speakers would make that mistake.
Seems simple enough: just replace whom with him, and if it sounds okay, you're golden. However, I did think of an odd case: "to whom it may concern" = "to him it may concern"; it makes sense, just sounds a little odd.
Now, it's just a matter of remembering this rule and applying it in my writing (and maybe even calling other people out, hehe).