France is definitely the most tourist-visited country. It's hard to find someone who hasn't heard of Paris or the Eiffel Tower. In summer Paris you'll see tourist crowds everywhere and very few locals.
Paris and the whole Ile-de-France region have a sophisticated and cheap transport network. For a 1-week stay since Monday, choose a Navigo Decouvert (zones 1-5) pass for €34.4 covering Paris, its suburbs, Versailles, Fontainebleau and other distant sights. Visiting only Paris places costs just €17.
Some passes provide sightseeing discounts. For 2 September days most museums are open free - probably the only time Frenchmen visit them.
France's basic currency is euro with €5, 10, 20, 50, 100, 200, 500-worth bank paper, €1, 2-worth coins and 1, 2, 5, 10, 20, 50 euro cent coins. Currency is exchangeable at banks, terminal and airport exchange offices.
Credit cards are accepted almost everywhere with Visa at the top. Mastercard (Access/Eurocard), Dinners Club and American Express are also widespread. CB (Carte Bancaire) is a French card as a Visa/Mastercard hybrid.
Most restaurants include the service fee (usually written down menus) in checks. It's common to tip waiters for good service. Taxists also expect 10% tips. Porters, door-keepers, guides and hairdressers often deserve €1-2, ushers and cloakroom attendants - €0.2-0.5.
France lets in up to 200 cigarettes (50 cigars or 250 g of tobacco), 1 l of 22+% alcohol (or 2 l of wine), 50 ml of perfume (or 250 ml of toilet water), 500 gr of coffee duty free. Customs officers will impose a fine or import tax for extras found. Drivers can bring in up to 10 l of gasoline, except in the car tank. Forbidden are drugs, pirated produce and fakes, child pornography, old coins and antiques, arms and some plants.