This one’s super easy to fix! Associate “then” with “when” and it’s a snap. They are only one letter off from each other. So, when you’re questioning whether you’ve got the proper usage, picture this:
WHEN are you going to the store?
Correct: First I am going to put on my shoes, THEN I’m going to the store.
Incorrect: First I am going to put on my shoes, THAN I’m going to the store.
Now, when it comes to THAN, try substituting compared with or in comparison to in place of it. If it doesn’t make sense in your sentence, you probably want to use then. Voila!