There are a few golden rules to getting by in France, and as one might guess, those rules deal primarily with etiquette and food.  In most cases, manners will serve you well and you will be well served if you use them.  Though the French aren't known for their friendliness, they are very formal and very polite.  I would argue that the snooty French waiter cliché is born mostly out of language barriers and cultural misunderstanding, though as with any other country one is bound to encounter a few sales cons every now and then. 

So.  Some facts, some advice, and some tricks for your French foodie experiences.

• It is perfectly acceptable in France to enter a restaurant or café and order only drinks, sit for hours, and not leave a tip.  This is true in most locations, especially those that have tables and chairs set up along the sidewalk outside.  However, if you sit at a table that has paper, a tablecloth, or place settings, the waiter will expect you to order a meal (rather than a drink and a croissant or something similar).  Although it's rare, some restaurants will expect you to order food no matter where you sit, but typically it will be obvious.  Restaurants with foreign cuisine (Indian, seafood, Mexican, etc.) like many of those found in Saint-Michel, for instance, expect those seated to order food.  Their seating areas are usually indoors or somehow offset from the sidewalk/street.
• Smokers are quarantined to outside tables.  Only recently has this become the case.
  
• Prices can change depending on where you sit, especially if you're only ordering drinks.  If you sit inside a café and order coffee, you may spend as much as 2€ more than if you ordered the same drink at a table outside.  The same is sometimes true for food.  By the same token, restaurants charge less for to-go/street food.  Part of this has to do with service.
• Service is included with the price of your meal, which is to say that your waiter has already been tipped.  However, it's not unheard of to leave some extra change after a drink, or a few small bills after a meal.  The fancier the restaurant, the more obligated you should feel to "tip on top," and leave your server a little extra cash.
• For cafés and more casual restaurants, there is no hostess.  Seat yourself and your waiter will come by shortly.
• Always greet your waiter, your baker, your cheese-maker, your neighbor, your cashier, and anyone else you speak with (the only exception being those you bump in the métro, to whom you should say "pardon" not "bonjour").  To enter a small market or specialty shop without greeting the owner or employees is very impolite, and this may be a large part of why Americans and non-French speakers are perceived as rude and insolent.  Likewise, upon exiting, you should say thank you and goodbye, especially if you've purchased something.  To say hello (depending on the time of day): Bonjour / Bonsoir.  To say goodbye: Merci, au revoir!  You may also wish someone a good day or good evening with Bonne journée / Bonne soirée. The more you Madame, Mademoiselle, and Monsieur people, the more formal and polite you sound.  "You're welcome" is De rien, or more formally (like "the pleasure is mine"), je vous en prie.  If the salesperson is someone in your neighborhood or someone you see frequently, you may extend your etiquette even further with "see you tomorrow" or "see you [day of the week]" to indicate that you appreciate their service and will return for business.  À demain, or à lundi / mardi / mercredi / jeudi / vendredi / samedi / dimanche.  Since my arrival in Paris I have been saying hello to every neighbor I pass in the hallway or on my way into / out of the building.  The more formal and polite I've been in restaurants and bakeries, the better the service I've received.
• Waiters in France differ from those in America.  French waiters are often career men, which is to say that people rarely wait tables on the side to make ends meet; for Frenchmen it is serious business.  French waiters are also more formal than American waiters, and will never introduce themselves ("Hi y'all, my name's Cindy and I'll be takin' care of you tonight.") as that would be improper.  Furthermore, they will leave you alone unless you get their attention; they will not stop by every five minutes to refill your sweet tea and ask if everything tastes okay.  There are no refills in France (and I can't imagine what sort of look one might receive upon requesting sweet tea), and it's a French restaurant--of course everything tastes okay.  By the same token, you must request your check.  Unless you have ordered only drinks, it will rarely be brought to you.  Again, this fits into French etiquette and formality.  Often the French take their time with a meal and talk at length when they've finished.  If the waiter arrived with your check alongside dessert, he would be rushing you or disturbing your conversation.  To request the check, you can get your waiter's attention with a little eye contact and a politely raised index finger while uttering the phrase, L'addition, s'il vous plaît.
• Table manners in France are pretty much the same, except both hands are kept on the table while eating (as opposed to the American one-hand-in-lap).  It's perfectly acceptable and even prefered during a meal to place your slice of bread next to your plate on the table.  The French will rarely put a serving of bread on the same plate with their meal (and you'll only see bread plates in nicer restaurants).
  
• If you bump into someone, need someone to get out of your way, or make a mistake counting change, etc., a little pardon or excusez-moi never hurt anyone.