I have found that the reception desk at your hotel can usually suggest places that are not touristy. Most of the better places to eat that are not expensive are on the side streets and if it look like a lot of locals are there, you usually can't go wrong. As for places to go and see, I think that just wondering around and poking your nose in whatever looks intersting usually satisfies me. The one thing that I regret not doing is going over to the island and seeing the glass works.