Paris

If you arrive at Charles de Gaulle-Roissy note the terminal where you arrive, it will be the same of your departure and this information, reported also on your ticket, will be crucial for you later. There are 6 major terminals, not very easy: 1, 2A, 2B, 2C, 2D and the new 2F. If you have at any time mistaken the terminal don't panic, there is a free shuttle that will bring you to the right terminal in a few minutes, if you know what's your terminal. Air France flights use mainly the terminal 2F. To reach the city the cheaper and faster way is the tube. To reach the tube station you can go by foot or you can take the free shuttle (just follow the indications, caution: there are 4 or more different shuttles marked with a different color) check for the one directed to the station (TGV and RER gare), it is the blue or the green one. You'll arrive at the tube and train station. Take your single ticket for Paris (8 Euro), follow the signs Paris by train, take the RER B. There is a direct train whose first stop is "Gare du Nord" and the second "Chatelet Les Halles" which is alternate with the one that performs about 8 stops before to arrive at the same station. The monitor on the platform will show you the times of approach. I usually prefer to wait for the direct train that is much less crowded than the other. Remember that yours is a first class ticket, choose the carriage with the yellow band. You'll arrive at the center of Paris in about 40 minutes, with your ticket you can also take any correspondence with the tube (metro). Take a look at the Paris tube map or search for the best itinerary at Ratp.
 

If you arrive at Orly it's a little easier, there are only 2 terminals: Orly ouest and Orly sud. Take the Orlival, an automatic tube that will bring you to the tube station "Antony" of the RER B and then in the center of Paris in about 25 minutes for 8,75 Euro, another time the cheaper and faster way to reach any place you want in the city. There is also a bus service, respectively the RoissyBus and the OrlyBus, I don't suggest it, the tube is faster and cheaper. Naturally if you have a lot of luggage you can take a cab, there are a lot of these at the terminals. This is the useful site of the Paris airports. Take a look at the Paris tube map or search for the best itinerary at Ratp.

If you arrive by car it isn't difficult at all to reach the center town, just follow the very well placed signs for the area you are searching for. No problem at all for the parking, there is a lot of garages everywhere, for a weekly pass you will spend about 70 Euro. Take a look at the Paris map.

If you arrive by train, there are many train stations in Paris, but they are obviously very well connected with the tube network. Take a look at the Paris tube map and search for the best itinerary at Ratp.