How much to know?

I am thinking about going to Japan next year to visit my friend (she's Japanese) who lives in Kyoto and was wondering how much Japanese should I know?

I only know a few conversational pieces, such as ''Hello'', ''How are you?'', etc. I also know how to count up to 999..haha. I am, though, teaching myself Japanese but haven't got quite far as to get into complex conversations or read the language. Any help or info would be great.

on how long you plan to stay there. If it's less than a month than don't worry too much. I'm guessing your friend can speak English so he/she will be there to help you out and be your guide.
If it's more than a month then learning some simple grammar structure and vocab would be best.