I've never done the tourist bus thing in Granada but I asked the company for price info for when friends visited me when I lived there. I know you can catch the bus (10 or 20 euros I think - sorry I can't remember!) on Gran Via right in front of the cathedral (less than 2-3 minute walk from Plaza Nueva). Look for the people wearing red shirts. Oh, I think there is a sign as well. And look out for the gitanos handing out sprigs of rosemary in front of the cathedral - the rosemary is free but the palm reading and other games they play are not. The tourist buses seemed to cover lots of places in the city.
If you're looking for things to do you can always go to the Capilla Real and the catedral, walk around the Albaicin and the city center, and/or sit around in bars all day - there are a lot, or visit the cartuja monestary. There is a tourist info center in Plaza Nueva. I suggest you stop by when you get there. Have fun.