Advice that is likely to work in most European places: know when is the tourist season. Visit famous places when it is not. During the tourist seasons, there are no shortage of very interesting places outside the crowded ones.

Vaux-le-Vicomte, which was the model for Versailles, is virtually unknown and a really nice visit. When crowd traffic jams happen in front of Mona Lisa in the Louvres, the medieval art sections, two stories above, are almost deserted despite very interesting pieces. Everybody wants to see Notre Dame, but there are about 100 monumental cathedrals in France.