Is it "Please join Paul and I" or "Please join Paul and me"? Do I lie down or lay down for a nap? How does violence on TV effect (or is it affect) young viewers? Do you insure or ensure that your seatbelt is fastened? Should you hone in or home in on your objective? Did the bride walk down the aisle or isle? Did the dog bury its or it’s bone? Is alright a word? How about alot? And did she pour over or pore over the details?
And how do you know when to put in a hyphen and when to leave it out?