If you decide to use a rial pass in Europe plan on arriving at the train station about 30 minutes before departure. Remember, a rail pass allows you to board the train but it isn't a reservation. In other words, it doesn't gaurantee a seat or sleeper. In Western Europe, high speed and premium trains require reservations. They are also reccommended for train trips lasting 3 hours or more, unless you like standing up. Lines that need a reservation are clearly marked with an "R" on departure sheets.
If you plan on sleeping on your train you have four choices. You can sit up all night in a regular train and greet the morning with bleary eyes. You can try for a foldout seat and hope it actually folds out (having enough room can be tricky), you can pay a little extra for a couchette or you can splurge on a sleeper.
Always keep you rail pass safely tucked away to avoid loss or theft. If it's lost and you have a police report you may get a partial refund when you return home. But it's so much better all around if you put your pass somewhere secure and safe.
Always get a map. These trains often make very short stops and it helps to know where you are and when you wish to get off. The map can be a lifesaver, especially if you're not fluent in the local language. Just know the spelling of the place you're traveling to (even circle it in red) and most of your fellow passengers will be able to point you in the right direction to continue your trip.