Once you are on the plane you are still responsible for your own security. Most things are out of your control, but you should take responsibility for anything you can.
Watch people on the flight. Any Terrorist? Which one is the Air Marshal? Which ones are military and law enforcement? Which ones are criminals? Start looking for all these people and you’ll learn to spot them.
On the plane I sit on the isle and an exit row when I can. I don’t get what I want most of the time. I do walk up and down the isle a couple times and look at my fellow passengers. This is more out of practice and rote then necessity. Airline travel in the United States is safer then ever. Not because of TSA, but because of the American people and other terrorist hunters. The American people will not allow another aircraft to be high jacked. But it never hurts to be prepared.
Aircraft are also the safest ever. Generally, air travel is the safest thing you do all year. But it never hurts to be prepared.
I pay attention to the safety brief. Find out where the two closest exits are and how the doors open. I keep my shoes on during the flight and have a flashlight in my pocket all the time.
Count seat backs to the exits. If the plane goes down, if you survive, now you have to get off. Grab your carry on that is next to which should have your first aid kit, water bottle, and your personal stuff. People will panic if the plane crashes. Your best bet is to crawl over the seats. You already know how far to go you counted. If you need to see use your light. But know when you turn on your light people will move toward you and then want instruction on what to do. They will think you are important.
We could go on forever, but will stop there. Just have a plan on what you will do if the worst happens and then pack accordingly.