any advice on traveling by train between frankfurt and berlin?

going in a couple of weeks, traveling on sunday.

dont exit until train has come to a complete stop

Check to see if it is more cost effective to get the Eurorail pass

Train travel in Germany is civilized, though a bit rushed in the actual station, as sometimes you have as little as 4 minutes between transfers. I don't know what kind of advice you're looking for, but all I can say is travel light (makes things easier), and at least have some rudimentary German under your belt.
You can take a shuttle right from the airport to the trainstation, and buying the train tickets was a breeze.
Also, talk to people :) I picked up a new way to do knitting, caught up on news, and made some interesting friends while on the train lol.

I spent last august in southern Germany - landed in Frankfurt and only took the train to Baden-Baden.

Don't pick flowers while the train is moving.

Yes, when the train comes to a stop in Hanover be ready to move your a s s , You have to go down the steps and up the other side to catch the east-west train to Berlin...and they don't wait a second....

travelling in germany is no problem. most expensive is to go by ICE train, its very fast (300 km/h) . Most cheap is it with the "Weekend ticket" only at sat. and sunday. But you need to change the train many times and you need VERY much time

I just booked a Eurorail pass for me and my daughter to travel in Germany. It was a lot cheaper than buying point to point tickets. You can jump on or off any train you wish as long as you have the passes. Train travel in Germany is safe and easy. Good luck!

Bring a good pillow and an alarm, so you wont miss your stop! The trains are very clean, comfortable and relaxing!

It is a fairly long trip depending on if you take the ICE or not -- and as previous posters said, the transfer time in Hannover can be a pain. If this is the only train trip you're taking, the Eurail pass will definitely NOT be a good option, because it will cost you at least twice as much. The happy weekend, or Schönes Wochenend Ticket, will only cost you 33 Euro, but it will take hours to cross the country because you have to change trains at the end of each federal state.
Make friends with the people around you, read the departure boards carefully, and have a ton of fun! FRA-BER is a nice route to take in Germany.