Dress professionally but comfortably.
Insiders repeatedly point out that those dressed nicely are most likely to get upgrades but people also just take professionally dressed people more seriously. Things go wrong – that’s life – but if you have to talk to someone in a position of authority for any reason you’re better off wearing a nice button up shirt and dress pants as opposed to pajama pants and that stain covered sweatshirt you’ve had since high school.
And for goodness sakes groom yourself! People show up to airports looking worse than homeless people.
Don’t be a dick to TSA or any airport personnel (ie gate agents). When you need something, they are much more willing to help someone who isn’t bitching at them, but rather asks nicely and treats them like human beings.
I can’t believe how many people bitch at the gate agents about a plane being delayed. Like the agent can do jack shit about it.
You can’t bring a bottle of water through security, but you can bring an empty bottle through security and fill it up once you are inside the terminal.