Paris (and France)
Politeness in Restaurants
In restaurants, it is polite (if not expected) to address your waiter/waitress as 'monsieur' or 'madame/madamoiselle'. Don't call a waiter 'garcon' unless you want to get kicked out of the restaurant. That is basically like calling him 'Boy'. Also, most meals in France restaurants can take at least an hour, so service might seem slow.
Do like your food?
In France, french speakers tend to understate things. If their food was really bad, they would probably say 'C'est pas terrible', or 'its not great.' Likewise, if it was good, they might say: 'C'est pas mauvais,' or 'it's not bad.'
A tip, sir
In French restaurants, a 15% tip is usually expected, but only if the words 'service compris' are written on the menu. It is also polite to leave an extra tip if the service was particularly good.