Riding the rails in Europe is a great way to see the countries. There is the scenery, the (relatively) stress free travel, and there is something to be said for falling asleep on a moving train. It's one of the few forms of travel that still retains its romantic imagery.
However, it's not just a case of romance and scenery. Like all travel, there are certain things to keep in mind.
If you book your ticket in Europe, it can be cheaper than buying it in North America. If you buy from the rail operators' website and buy a no-refund, no-change-of-date, no-anything ticket, then you'll have scored a deal.
Divide and conquer
The entire train may not arrive at your destination. Seriously. Unlike VIA trains, where the whole train stops at each station and people depart, European trains may leave or add cars as they travel across countries. Ensure you're on the right car.
The great train robbery
Thieves like trains. There's something about a train that makes people lower their guard, and thieves love that. Secure all your luggage, not just your suitcase. If you have a backpack, attach it to the overhead rack. It's easy for a thief to snatch a bag and disappear, especially if you've been lulled to sleep.
Cross the map
Trains make it easy to visit another country. The Eurostar from St. Pancras in London to Gare du Nord in Paris is two-and-a-half hours. You could go to Paris for a day. Two-and-a-half hours doesn't even get you to Kingston from Toronto. (Well, if you're speeding it might.)
Keep it timely
This website should be your best friend if you're travelling Europe by rail: SBB.ch. It has the timetables for all of Europe. And yes, for those wondering, it does come in English. Bookmark this site.
The early bird gets the bed
If you're booking a cabin or sleeper for an overnight trip, book as far in advance as you can. Couchettes can be booked closer to your departure date but all of them do fill up fast. You will have to pay an extra fee for these.
Meals on rails
Bring food. Don't expect a buffet car or even a food trolley on some trains. Even if there is a food trolley, the food may not be appetizing: squishy bread with indeterminate filling (possibly egg). Hit the stores before your trip and stock up on at least one meal -- buy meat, cheeses, fruits, biscuits and maybe a small bottle of wine. Then tuck in.
Ride like royalty
Try first class. Yes, first class can be expensive, but check out the prices instead of skipping them and going directly to economy. Since plane travel is also fast and cheap(ish), first class by train may only be a few more pounds or euros. If you're travelling for hours, maybe it's worth it. Second class is also pretty comfortable, thanks to advances in newer trains.
Tricks of the trip trade
There are multi-trip, one-pass deals if you do your research and ask beyond the Eurail pass. Some tickets will let you stopover in a city on your route. You can wander for the day, or even overnight, before getting back on your journey.