Ever since high school I've wanted to hit Europe with nothing more that a Eurail Pass and a backpack. I'm perhaps 40 years late but I finally managed to do this. I just returned yesterday from 10 days in France, Germany, Belgium, and Luxembourg. Overall I had a great experience but here are some tips, meaning things that I wish I had known!
First, I can't imagine wandering Europe today without a roaming data plan. Train schedule booklets are no longer printed and many (most?) train stations don't even have the big schedules displayed on the walls any more. Everything, everything, is now done online. Open Wi-Fi access was hard to come by, the most reliable being what was available in hotels. After a day or two I managed to get my iPhone plan enabled for roaming data and that made the rest of the trip possible. I'm not exaggerating.
Second, it is now almost essential to have a European-style credit card with the embedded chip. Our lame American cards won't work in the automatic machines. Thus, if you need a train ticket you have to see a clerk. And since the machines are the main way to purchase tickets nowadays, the number of clerks have been reduced. I routinely stood in line from anywhere between 20 and 40 minutes to get a ticket. Which brings me to the third point.
I'm not convinced that a Eurail Pass is the right way to go now. Nearly every trip required a reserved seat or a supplemental charge. I couldn't arrange these things from the machine, having a Eurail Pass (even if I did have a European credit card), so I had to stand in line. I suspect I really didn't save much, if anything, by having the pass. And I would have covered more territory if making travel arrangements had been easier.
Finally, as an independent traveler I found it really essential to have some rudimentary language skills. Prior to my trip I spent several months brushing up on Spanish (which I didn't have the chance to use), and adding a bit of proficiency in French & German. I bought the Rick Steves phrase guides, which are good, but I'm really partial to the Penton Overseas, "Learn in Your Car" CD sets. I pretty much mastered the first two CDs from each set and that proved adequate. I started every interaction using the foreign language and no one was ever rude to me even though we often switched to English. One high point occurred in Bruges when someone thought I was actually a French speaker!
I could mention many other things like listening to the Rick Steves podcasts about everyplace I was interested in visiting, discovering Ibis Hotels, or all the great advice in the Back Door books, but I'm sure that's old news around here. All-in-all I had a great time, fulfilled a life long ambition, and I'm grateful for all the tips & advice that I've picked up from Rick Steves over the years.