Make sure the airport you think you are flying from/to is actually the airport you are flying from/to:
Walking in uniform through the terminal at Glasgow when a gentleman rushed up to me, shoved his paperwork in my face, and asked where to check in for a Ryanair flight. Was slightly perplexed as couldn't remember seeing a Ryanair aircraft at Glasgow - closer inspection of his paperwork revealed the words: Glasgow (Prestwick).
I assume he missed his flight!