Don't bother to lock zippered suitcases. You can pop a zipper with a pen and drag the locked zipper pulls around the bag to close them back up. TSA also pops the lock if you have questionable content in your suitcase.
Bring Your Own Headphones
The headsets that are given to you are not new, despite being wrapped up. They are taken off the flight, “cleaned”, and then packaged again.
Remove Old Flight Tags
It is just common sense; the reason some bags miss their flight or get misrouted is because passengers don't remove old tags. It confuses handlers as well as the conveyor belt scanners.
Be Kind to Employees
The nicer you are to them, the more they do for you. Ran out of beef? Ask politely and we will get you a fillet mignon from first class. Is your neighbor noisy? Tell the flight attendant nicely, and they might be able to get you a better seat.
Be nice to the ticket agent and they will pretty much always let you get away with overweight bags.
Buy and Fly on a Tuesday
On average, the cheapest time to BUY a ticket is Tuesday afternoon. The cheapest time to FLY is Tuesday, Wednesday, or Saturday. This applies to US flights in my experience. Of course, there are some exceptions.
Put Your Pet’s Name on the Carrier
If you checked your dog there's about a 30 percent chance it's terrified before it even gets on the plane, who knows how scared it gets during the actual flight. Bag room agents will usually try to comfort a scared animal, but all they can really do is talk to it, so if you write your pet's name on their carrier it usually helps a lot.