A good starting point is the Michelin Guide to restaurants for Italy It identifies the "top" restaurants (1-3 stars) but it it also identifies many non-starred but solid places to eat. The "bib gourmand" category is a particularly good one as it recognizes places where one can get a good meal at a relative reasonable price (for the area). As everyone's idea of what is a "great" restaurant can vary, it might help to look over some alternatives to see which cater to your taste and budget. Michelin is probably not the best source for the newest trendy restaurant but they do recognize the time-tested. Another good site (and app) is thefork.it - it's a little more likely to find the trendy places but it also doesn't screen out poor choices as well.

Sure, Michelin will miss some good (particularly newer) places but I've never been disappointed in their recommendations and it is my go-to resource when I'm in places that aren't in my backyard. And when I'm traveling I don't need a huge number of places to try but I do need a quality set of alternatives as there is nothing sadder than wasting a bullet by having a poor meal.