I wholly agree with Maleficent's advice. I occasionally read my journal that I kept during my trip to europe [over the summer, 3 weeks]. It reminds me a lot of what I forget, and reminded me of all the good times I had - it's a great pick-me-up
Don't be afraid to take a lot of pictures too, if you want to. Also, I'd recommend not to cave into American culture there. For example, some of my fellow travelers went to Mcdonald's in France for a snack, though they had a few other choices to eat from.
Be Open and don't be afraid to ask questions !