Some really good advice here.

Just a couple of bits to add:

As others have said, be prepared! Make sure that you've got all the technology you need for the journey (tablet/phone/headphones/chargers etc), along with anything else you might need. I'd also suggest that you have some basic medicine with you (paracetamol or similar) just in case, the dry air on planes can do funny things, I often end up with a headache on longer flights.

I think this was mentioned elsewhere, but I'll say it again. It's highly unlikely that the airline will lose/delay your bag(s), but it does happen. I always pack a change of underwear and t-shirt in my carryon, just in case.

I know this is easier said than done, but try not to worry too much. Millions of people fly every single day and absolutely nothing happens to them, air travel is after all, the safest way to travel. Be prepared, know where you are going and how to get there and you'll be fine.

Also, I wouldn't advise you to take any kind of sleep aid (ambien etc). I tend to avoid it, but that's just a personal choice, thousands swear by it. If you do want to take something like that, perhaps try it at home first and see what effect it has on you; not a good idea to try something for the first time on a plane.

Relax, you'll be fine. Hope you have a memorable, enjoyable trip!

Ps. Please report back and let us know how you get on!