For me, the best place to start conversations was in onsen. I guess being naked and stuck in a steaming pool together helps. :D
I actually didn't have particularly hard time talking to people. I found them extremely friendly and I often got really positive reactions to my Japanese. Just use natural situations, like asking for directions, or if you need to get something read for you, like a bus map or time table. If you're waiting together, or taking the same transportation, you will get a better chance to exchange a few words.
Good luck and have a nice trip!