I've traveled a bit, I've been to Spain, France (and extension in the same trip to Germany), the U.S. a few times, and Canada. I adore traveling and getting lost, most of these cases I take week-two week long courses since it comes out cheaper and you get discounts.
So ok what can I say from experience:
-First off, being a US citizen gives you a lot of easy breaks when it comes to customs (It's a little unnerving but you get treated better than others I've noticed). Regardless they can be killer and when I was flying back from Canada it was a terrible trip as the JFK customs kicks you right out of the airport and if you have a connected flight you have to go through customs ALL OVER AGAIN. (So if you bought a few stuff in the airport, then suddenly you have "too much with you" and might be asked to pay extra. This is what happened to me when my bag broke back in Vancouver)
-Travel lightly, just go to any laundromat in the city you're staying if you need to, but you'll be thankful about it. You can take a carry on or a large backpack and it'll be less things to worry about.
-Roll the pants, do not fold them, and you can also place half-folded shirts in and you save yourself luggage space.
-If you're like me....you'll buy a lot of things. Especially books. If you're on your way back (again depends on the country) you're better off bringing the heaviest things with you and mailing the lightest since they charge by weight and space. (When I was traveling this summer, I mailed my clothes and packed 35 books on my carry-on. Came out LOADS cheaper)
-Swords and weapons CAN be bought and brought with you but they have to go on the bottom of the airplane and they have to be inside a box and wrapped.
-Tickets are usually cheaper about 120-90 days before the travel but check every now and again for prices and disable cookies in your browser for the best offers.
-If your passport is expired, get one NOW. They say it only takes a couple of weeks but when I was going to France I cut it close at just 2 days away before traveling and I was super stressful. Do not recommend.
-Learn to sleep while sitting down. (Makes airport experiences more tolerable, neck pillows are your best friend) Also as soon as you land and it's a connected flight, find your gate and explore around. Don't buy the first thing you see if you're hungry, you might be surprised at some specials in other terminals.
-Buy bubblegum and chew on it during take-off and landing, it helps your ears without popping them.
-Study country customs. Know what's ok, when/if to tip, some basic words and questions. Always ask in their language if they speak yours first before asking for directions. People will be thankful and will be more lenient to help you.
-Don't convert ALL your traveling money into their currency. Calculate more or less what you can use (credit cards only for emergencies) and if anything then go to a Western Union (but be mindful of their sometimes scamming rates) or go to a bank that may share chains and extract money from there (fees can sometimes even be cheaper than conversion stores go fig.)
-I usually stay with friends, but if not, hostels are pretty great. People your age, cheaper, you can ask them of places to hang out.....cheaper.
-ALWAYS pack a towel (Hitchhiker's Guide makes it clear haha), portable power converter, and a jacket. Even if they say it'll be hot, ALWAYS bring a jacket.
-Phone on airplane mode. But bring it with you nonetheless, it's an MP3, can hold ebooks, status updates, it can very well replace a computer if it's a good phone. But NEVER leave it unattended nor in a back pocket.
I hope this helps and have fun!