How old are you?
1. Spend more time in places like Lisbon and Budapest and less in places like London and Rome.
2. Bring a roller bag, I carried everything on my back for a month and it was hell.
3. Look for laundry mats before you travel, some cities don't have them
4. No AC in europe and it rough ridin' blows in the summer
5. Airbnb will save you a ton of money
6. eff the trains, especially overnight ones. Your time is expensive over there, flying is faster cheaper if booked in advance.
7. Get ready to eat like crap. I haven't the slightest idea how european food got a positive reputation (I have a theory) but it's really pathetic and meats suck.
8. Visit some crap hole like Belgrade or Bratislava and stay in the cheapest hostel possible. It will really put your life in perspective.
9. Buy and international phone plan. Constantly looking for free wifi will drive you nuts.
10. Euros typically have false delusions of worldly competence and grandeur because they constantly tell each other how great everything around them is and they think visiting other european countries makes them just as cultured as visiting countries on other continents. The reality is Europe is closer to Mexico than the United States and everywhere I have visited in east Asia blows it out of the water. Have fun sipping your 5 euro tap water *No refills*