Travelling in the off season is the best way to score deals and avoid mobs of tourists, but you can't always travel in the off season. Beat the tourist crowds and get a more intimate travel experience by staying where large groups just won't fit because amenities can't accommodate them. Image from blok70.
You won't be able to avoid crowds at popular sites or during the day, but Rick Steves explains how you can escape in the evenings:
Popular day-trip destinations near big cities and resorts such as Toledo (near Madrid), San Marino (near huge Italian beach resorts), and San Gimignano (near Florence) take on a more peaceful and enjoyable atmosphere at night, when the legions of day-trippers retreat to the predictable plumbing of their big-city or beach-resort hotels. Small towns normally lack hotels big enough for tour groups and are often inaccessible to large buses. So they will experience, at worst, midday crowds.
When I visited the southern Italian coast, I used this method and stayed for most of my trip in Positano rather than a larger city like Salerno or Naples. Since the town's streets are too narrow for large tour buses, I never had to deal with crowded restaurants, beaches or accommodations. You can do the same by staying in smaller towns that are close to your target destination, then see the sights on day trips.
When to Go to Europe: Timing Your Trip [Rick Steves]