1. Never forget your camera... you'll regret it!
2. If you know you have a long plane flight, and want to use your phone for games and music, bring along an extra cell phone battery, most airplanes don't have electrical plugs.
3. If you're going to a different country, remember to bring along/buy an electrical converter, otherwise you won't be able to plug in any of your chargers!
4. Don't wing it, buy a travel guide and use it to your advantage! Learn about historical sites you have never heard of and visit those small, amazing museums that don't show up on the map! I recommend all of the books Rick Steves has written, he has found hotels, restaurants, museums, and tour companies within every price range.
5. If you don't speak the native language, don't rely on your smart phone for the language translator, it needs some type of wifi or 3G, which you won't have in a different country when you're on the go, learn some phrases that will help you (thank you, please, hello, good bye, where's the bathroon, etc.).
6. And most of all, HAVE FUN! :)