A: Anyways is not a word. Instead, try anyway. Affect means to influence, while effect means to cause. That's right.
B: Biweekly means every other week. Semiweekly means twice a week. Also, between introduces
two items, while among introduces more than two.
C: Imagine eighth grade: You are able to go to the bathroom (Can I go?) but you should get permission first (May I go?). BONUS "C": Complement vs. Compliment.
D: Dived, not dove. I dived last week. Simple and elegant, and though it may not sound proper, it is.
E: Ensure means to make certain. Insure to to cover with insurance. BONUS "E": Except vs. Accept
F: Funner is not too fun after all. People will laugh at you, not with you.
G: Good vs. Well: Good is an adjective that means something is as it should be or better than average. Well means suitable, proper, or healthy.
H: BAD GRAMMAR: "Hopcfully, I will..." GOOD GRAMMAR: "I am hopeful that..." You're not alone on this one.
I: Irregardless Is not a word. Try its helpful cousin, regardless. BIG BONUS "I": There is no possessive form of its. It's mean's it is. BONUS BONUS "I": Infamous vs. Famous.
J: Jibe means to shift direction. Gibe means to taunt or sneer.
K: "Kind of" is not to be used as a substitute for rather. Restrict it to its literal sense: "Amber is a kind of resin."
L: Use Fewer for individual Items. Less is for bulk quantity.
M: It's Emcee, not M.C. Hammer Time.
N: Nor follows neither. (Embrace your snooty relatives.)
O: Online Is one word with no hyphenation. (By the way, it's a World Wide Web now.)
P: Penultimate means "the next to last," not "the most excellent."
Q: Quotation marks go outside the period at the end of a sentence. BONUS Q: Queue means to stand in line, and that is how to spell it.
R: Renown is a noun. Renowned is an adjective. It's tricky.
S: When speaking, try to avoid "supposibly." It's actually not correct.
T: To vs. Too vs. Two. There vs. Their vs. They're. Ask your parents to sort it out.
U: Unique is a word that cannot be modified (ie. the most unique).
  V: Via should only be used in connection with travel or shipping (vs. "by means of").
W: Whence means "from where." To say, "from whence," is redundant. BONUS "W": Who vs. Whom and Was vs. Were.
X: Never abbreviate Christmas to X-mas, or any other form.
Y: Your vs. You're. (Are you getting the hang of this?)
Z: Zeros vs. zeroes. Remember Dan Quayle's potatoe?