The only "long distance train ticket" directly from Munich to Prague you can print is actually a bus ticket. Tickets for the Bahn Intercity bus directly from Munich to Prague can be purchased in advance as Savings Fare Tickets. These tickets starts at 29€/person. Time is about 4½ hrs.
You can go from Munich to Prague starting with an ICE to Nürnberg, but the next leg is another IC bus from Nürnberg to Prague. That connection would take more time (5½ hrs) and the starting Savings Fare is 39€.
There are 3 direct trains (ALX) per day from Munich to Prague (4 actually, but the first one leaves at 4:55). They take 5¾ hours. The fares using a Bayern-Böhmen ticket to Pilsen and Czech Rail tickets from there to Prague is about 38€ one way for two. The Bayern-Böhmen ticket cost 30,50€ for two and can be purchased any time from a Bahn automat, even right before departure, for that price.
If you really wanted to get advance purchase Savings Fare tickets, you could ticket Munich to Nürnberg by ICE, to Dresden by RE, then by EC to Prague. Those tickets start at 39€, but the trip takes over 9 hours.