I can’t tell you how many times I see than and then mixed up. Yes, they sound similar… not exactly alike, but similar. Than rhymes with pan and then rhymes with pen. See? Two different, separate words. Most of us use them correctly when we speak…. just not when we write. How do we remember which is which? It isn’t too hard.
Than is a conjunction (Remember “Conjunction Junction… what’s your function?” from Schoolhouse Rock!) that is used when you are comparing something. I like cheesecake better than strudel.
Then is is an adverb (Remember “Lolly Lolly Lolly Get Your Adverbs Here – Schoolhouse Rock!) that deals with time. You use it when you want to tell the order in which something happened or that you should do things. You see it a lot in recipes. Plate up the noodles and then add the sauce.
All you really need to do when you are stuck in the Than or Then quandry is ask yourself if you are comparing something or telling the order in which something occurs. If you find you are not making a comparison, use then. If you are, use than.