I think the most important thing to know before you travel to another country is a general list of what is going on while you are there and things to do. Of course you are going to need to prepare first (train pass, museum pass, cost of living), but the main goal of travelling abroad is to enjoy yourself, so figuring out the best way to accomplish this is incredibly important. It is much easier to find out when festivals are or what are the best tourist locations before you enter the country because you run the risk of simply being unable to attend if you find out when you are already there. However, it is often not the best strategy to have the whole trip planned out in meticulous detail. This can make you feel rushed and stressed at a time in which you should be relaxed and having fun. My advice would be to find a few items that you absolutely want to go to and any time restrains on those things, then have some other possibilities in the back of your mind.