1. Buy Tickets Online: In cities with big tourist attractions that require tickets, it's always a good idea to try and buy the tickets on line. Most of the time you can even download a QR code onto your phone so you don't have to keep track of papers! It can be cheaper too!
2. Use Hop-On Hop-Off Buses: One of my favorite things to do is use a hop on, hop off bus when in a big city. It's cheap transportation and you get a to hear about landmarks you may not have known about! They are normally around 30 euro, which isn't too bad! These are easily an entire day.
3. Leave a day/afternoon free for exploring: One of my favorite parts about traveling, other than the food, is wandering and experiencing residential neighborhoods of cities. You find great gems, cool gifts and even a hidden landmark.
4. Book a shuttle or look into using public transportation: Honestly after traveling in a plane I don't want to have to deal with finding transportation. One week before I travel I look to see if there is a shuttle service that can take me to and from where I'm staying, or public transportation that's easy to navigate. In Paris, a shuttle service saved my 30 euro. We used a taxi in Berlin because it was easier and more worthwhile than public transportation. Don't always use a taxi as default!
5. Take pictures of monuments with Yourself: I didn't do this too much with other trips and I definitely regret it. This semester I took lots of pictures with my friends and myself because in 5 years I'll want those. Artsy pictures can always be bought.
6. Be aware of your surroundings: Pickpockets are real in Europe, though some cities are worse than others. Be aware of that when you're traveling, and make sure to find a suitable bag. Personally I prefer a crossover with a flap or a zipper because I can keep it in front of me with my hand on it. Don't be over vigilant but don't be oblivious either!
These are my top tips for Europe! What are yours? Where have you been? I've actually added more cities to my bucket list!