Prior to our trip we did a lot of planning and research. One of the best things about Rick Steves' Tours are their wealth of information. Even if you are not going on one of their tours there's so many helpful tips provided on their website that can help you plan your own trip. After finishing our tour we now feel would could go back on our own and have an amazing trip from everything we've learned. We highly recommend checking out Rick Steves' travel tips section on his website.
A couple tips we can provide is travel light we carried a small roller suitcase and a backpack for our day trips. The tour moves quickly from point A to point B so you can have the most of each location. So you don't want to be dragging a huge suitcase down the street. Remember you can always buy items you may need while you are there. Also we would recommend carry some cash or always check if the restaurant accepts credit cards or not. We noticed that in Vienna that a lot of the restaurants we went to only accepted cash which seemed surprising being a city, but now we know :)
One more tip! Download the Google Translate app and download your countries language prior to your trip so you won't have to use your data when you are roaming. It is a great app that can translate the countries language to yours. Also you can use your camera and point it at the signs and it will instantly translate. Now it isn't perfect, but is very useful to get the idea of what a sign says or even your food menu.
Another thing we did prior to our trip was watch Rick Steves' travel talks. It had great little tips such reading signs and figuring out the train system in Europe which was one of our concerns when arriving in Germany. After watching those we felt a lot more comfortable when we arrived and was exactly what he described.