To add my 2 cents to this, there is a lot of good advice in this thread, but I would specifically highlight two aspects that other posters mentioned.

1. Get to the airport early. There are many things that you need to do once you get there, but none of it is difficult if you have the time to do everything in a relaxed manner. People tend to make mistakes when they are rushed. And if you have a lot of extra time, don't worry, airports are interesting, particularly if you have never flown before.

2. Don't worry about forgetting anything. The only real essentials are your wallet and (if travelling somewhere where it will be required) your passport. Anything else that you forget can be purchased at your destination.

Those two factors are, in my view, the most important for keeping the stress levels down.

Have a great trip!