Care to share some general travel advice for me and my friend?

Additional: Our main priority is to avoid wasting time, so no boats, coaches or trains unless it takes us past something we want to see.

This sounds like an exciting adventure!

Other Advice I do not want to come across as pessimistic with this answer, but if you are meeting both online friends for the first time, hope for the best and expect the worst. There is always the chance that one or the other will back out of the meetings at the last minute. Prepare for a Plan B in case you find yourself on your own for this trip. You might also find out that the travel friend’s habits drive you insane. The happened to a friend.

Good Places to Visit It is difficult to answer without knowing the specific locations. If what you mean is more of a general question, then for France, Paris is the place to go. I would pick Rome over any place in Germany, but of course it depends upon what you want to do and see.

Safety If you are only traveling in Europe, you two should be quite safe. Select wisely where you stay, and keep your valuables, like a passport and money, in a waist belt under your shirts. Keep a record of your passport numbers, as well as any credit/debit cards you have and the contact information in case they go missing or are stolen. You might want to notify your embassy where you are traveling. In some countries, this can be done online.

Travel Problems There is bound to be some problem along the way. The worst are when there are air flights involved. One might get delayed or cancelled. Getting robbed is another (see above). An unexpected natural or man-made disaster is also something to consider. A friend from the UK got stuck in another country when the Iceland volcano forced airports all over Europe to shut down for several days, and she ran out of money.

Good Places to Visit I agree with Pfeffer that Rome wins out over Germany, but may not be conducive to not spending a lot of time traveling, especially if you’re planning to be around central Europe because Rome takes some time to travel to by train since you have to go through the mountains. Florence is also worth seeing, but it’s also a long train ride. Paris is the place to go if you want to see a lot of famous artwork whereas I imagine Germany would host more impressive architecture. If you want to eat fantastically, go to France or Italy.

Safety Also make sure you let your bank know you’re traveling so they don’t freeze your account on the presumption that someone has stolen your card and is using it in another country. Try not to look or act too much like a tourist – muggers/pick-pockets are more likely to single out people who obviously don’t seem like natives. I wouldn’t worry too much about that, though. I’ve never had a problem. Just be polite and use common sense.

Other Advice Restaurants in highly toured cities are terribly expensive. If this is a concern for you, go to a grocery store instead (the people who actually live there have to eat too.

Also, I know you don’t want to waste time, but if you walk places there will always be something cool to see along the way.

In addition to all the great answers above:

Safety: Even if Europe is supposed to be safe, beware of pickpockets when being in the touristy areas, on markets, in the tube, in crowdy bars. This is a thing you should be aware of.
Also I like to keep a paper with copes of my ID, my health insurance and my visa card and important phone numbers deep down in my backpack (or suitcase if you don’t travel with a backpack) in case my wallet gets stolen.

Other Advice: ask locals what to do. Mostly you find a nice waiter or a guy that works in your Hotel/Hostel that knows the best way around the town. It’s ten times better than to rely on an outdated map.
Also in many big cities they have tours that are made by some freelance people. They are always great, because at the end you pay only as much as you like, depending on how much you liked it.

Good Places to Visit: If you are in Holland, take a train to Brussels. It is much faster, cheaper, interesting than taking a plane. They have awesome food (waffles, french fries) and the city is awesome.
I’d also say Paris is a must. Climb the Eiffel Tower to the second platform and then take the Elevator. It is like the best thing ever. Or do a night picnic in front of the Eiffel Tower, and watch the light show. (safety beware of the guys in front of scare coeur. They tie wristbands to your arm without asking an then you have to pay 10 bucks for them)
If you want to cover germany, go to Hamburg and dance a night through on the Reeperbahn (red light district with an enormous amount of clubs/bars/pubs), or visit Berlin with all its history. Or Munich – which is like cliché Germany.
If you’re going to Italy besides Rome I would advise you to go to venice. It is super expensive, but since the city is sinking it might be your last chance to see it ;).

A last general piece of advise: don’t run. don’t try to be in every city and don’t really see it. Just take your time to get to know the place you’re right now. If you do 10 cities in a week, you’ll be feeling like you have been nowhere. And keep a travel blog. They are great memories with pictures and everything. And a great way for your friends at home to see what you’re doing. http://www.fuzzytravel.com/ this one is free and easy to use.