As I have been thinking about our trip, I was thinking of things that aren't told in travel guides but I think are key to having a good time.

Sense of Adventure. One thing that was brought home is that we have to have a sense of adventure, a go with the flow or a "when in Rome" mentality. For all the carefully planned itineraries, things happen- lines are longer than expected, train workers go on strike, the weather may or may not cooperate. Actually I kind of like when things don't go as expected or a new challenge occurs. It provides an opportunity to test one's mettle. Will I fold in despair or rise to the challenge? Many times the solution and its experience is much better than planned.
Remove one outfit from your bag. Even though each of us had only one carry-on, I still brought more clothes than I actually wore. Partly it was due to the weather. I had looked at the temperatures for Rome, Florence and Vienna before I left but the actual weather was slightly different. Not that an extra shirt or skirt took up much room, but it seems once you are schlepping bags through airports, onto trains, buses, up and down escalators, stairs and down cobbled streets every little item seems to gain extra weight.
Wear good walking shoes. I am so glad that I brought the shoes I did and that I had three pairs so I could rotate every day. I had some goals in mind. Closed toe because walking through the streets can be a mess. One pair was a comfortable slip on which was helpful with airport security. There were places in Rome that I was grateful for the toe protection. I needed a pair that would be good for bike riding. My walking pair that I used on our Oxford trip was perfect- light weight, stylish and rubber soled. I also didn't want shoes that screamed ugly American. I found a nice pair of wedged, espadrille type sandals. They were stylish but I could navigate through the cobbled streets fine.
Carry a water bottle with you. We always set out each morning with full water bottles. You never know where you can find water. Some of the "touristy" places really soaked you for it. We did find water pumps throughout Rome. The first time we saw a workman stop and fill up his bottle we wondered, is it legit? It was an old pump, had a greenish patina on it. But it was cold and fresh. Turns out it is part of the Roman aquaduct system. Of course while I was drinking from it, I turned to my family and asked, "Do you think they upgraded the lead lined pipes?"
If you see something, buy something. We visited one of the local Saturday markets in Florence. The choices of fruits and vegetables were amazing! Fresh, colorful and tons of variety. At the market they also were selling household wares and clothing. Some new, some used. There were some new Italian linen pants and shirts that were very inexpensive. I toyed with getting something but decided against it. After seeing the same type of items here at the states, should've gone for it.
Purchase online tickets before hand. There were some place on our itinerary that we knew we wanted to visit. We weren't quite sure of the day but we just decided to fill in our plans from home. We noticed on our last trip, if you schedule online that many times the cost is cheaper, you don't have to wait on line at the ticket booth and you don't have to worry about money.
Eat where you see the locals eating. We had a wonderful dinner in Vienna (actually we had many wonderful meals, cannot think of a bad one) at a local beer garden. It was a local brewery and they had simple wooden tables set up under the canopy of a tall tree in their courtyard. The ground was covered with fine stone that crunched as people trudged in. People were greeting one another, coming from a day's work or celebrating with friends. There was a Vietnamese family sitting at the table next to us. During the meal another table dweller approached them, asked where they were from and explained that he was in Vietnam. There were shared stories and drinks among them. Quite a picture of community.
Try the language. Well, my experiences with languages are not so great. But I did make a noble effort. Of course, every time I said thank you, it sounded Spanish.
Visit smaller museums or take a day trip. We visited a very small museum in Florence featuring Leonardo Di Vinci. I think it might have been geared for kids but it was just up our alley. They had prototypes of the different machines and inventions that Di Vinci drew in his notebooks. Plus, they had a very interesting movie about his life.
Read up about places. Ideally it is best to read up about a place before going there. It makes the entire experience so much more rich and full. But, as in our case, we didn't have too much time before hand to do that so I am reading now. The benefit in reading afterwards is that when places are described I can see them in my mind's eye.

What about you? What travel tips would you offer?