(Note - this was true in the 92-93 time frame, but since then there has been a backlash against the ``corruption'' of the French language by English, and especially ``Amercianisms''. Ask your travel agent or a French-savvy friend about the current situation.)
Nevertheless, it is a good idea to speak at least a little "French" ("Francais"). The French will be appreciative of any attempt to speak their language. Even though they may suggest you speak English, you will have made an impression by trying (although if you totally mutilate the language you are better off slitting your wrists now).
Any of the better guidebooks will give you an acceptable introduction to conversational French. It is also a good idea to have a decent English-French/French-English dictionary along. Study the guidebook before you go, and have at least a few key phrases memorized. Try to practice with someone here who knows pronunciation; French is a maddening language to the USAian ear.
The trick with French (as with any language) is to get as quickly as possible to the point at which you quit translating, and begin thinking in that language, at least as much as your vocabulary allows. The real fun then begins when you return home, and answer the wait-person in French at your local Tex-Mex restaurant.
I found the French to be a very friendly people. They were generally more than willing to help, answered all sorts of questions, and were quite patient with my pathetic attempts at communicating in French (the lingua franca, strangely enough, of France). [My wife didn't find them as friendly.]
It is, however, a totally different culture than what most of us are used to. Some aspects of Paris are those of any big city - pushing on the subway, etc. When you enter work in the morning, be prepared to shake hands with everyone you know and say, "Bonjour, ca va?" (In Texan, this translates to "Howdy, pahdnah! Ya'll doin' all raht?") At some point late in the afternoon (which I never pinned down) you can say "bonsoir" ("evenin', y'all") instead of "bonjour". BonXXXX greetings are also farewells.
Tipping in restaurants is redundant unless the service or food was "tres tres magnifique" ("it knocked mah socks off"). Unless the menu says otherwise, a 15% gratuity is included in all prices. Most menus will probably say ``Service compris'' (which looks like a Jerry Lewis in Japan joke), meaning ``Service included''. Tipping of cabbies, doormen, etc is pretty much as anywhere else. If your food/service in a restaurant is so awesome you simply must tip, do not just leave it on the table. Hand it to the appropriate individual with a handshake and a "merci" ("thanks") or "merci beaucoup" ("thanks a heap!")
"Toilettes" (twah-lay') is one of the signs you had better know, along with the Seven Major Warning Signs of Intestinal Parasites. (Nevermind, that's for Central America.) Beware, however, that public toilets may not be "American style". Some of them are simply ceramic latrine trenches. These have a place to park your feet, and you squat over the hole. The flush valve actuator may be one of billions of types, but is usually the thing about 3 to 4 feet directly above the hole, attached to the wall, regardless of what this may look like. Simply push, pull, twist, pound, and so forth until something happens. Some toilets will be marked WC (for Water Closet, or its French equivalent). (Beware. My wife ran into a couple of these which were apparently adjusted to spray the user like a well-aimed garden hose!)
The French love doors. This is evident in their subways, and in buildings such as some of those housing IBM and Bull. At the Bull Massey site, in the space of maybe 150 feet, you will pretty much emulate Maxwell Smart in the intro sequence from Get Smart. The only doors missing from the sequence are garage-type doors. The IBM Tour Descartes (``Descartes Tower'') includes some Enterprise-style transporter booths. Self-powered revolving doors are also common.
Subway entrances and exits include every type of door actuator known to humankind. This includes turnstiles, pressure-actuated doors, push-style doors, saloon-style doors, and most everything except nuclear-powered, magnetic-anomaly-triggered iris style doors.