I use "then" way too much when trying to teach something. You don't see it as much because I always read my posts before I click "Post". I try to correct my mistakes and goofs, but I'm not always successful at finding all of them. Sometimes I wonder where people are looking when they type in a post. Aren't they looking at what they are writing?
The editor of our newspaper says: "I bought a ticket for my wife and I." Did you buy a ticket for I? Take the "and" out and see if it works. Our club president always says: "If you have questions, see Cindy or I." Makes me cringe every time. You don't say: "See I."
Usually I is at the beginning of a sentence and me is at the end. Not always, but mostly.