The public transportation in the city of Paris is govern by RATP (Régie Autonome des Transports Parisians). They run the busses, Trains and the subway system (Metro).
The subway system runs on 15 different routes connecting Paris with its outlying suburbs. This operates from 5.30 to 1.00, and most of the popular area will be covered and the most efficient way to travl around Paris. Refer the Metro maps, which are available in most of the hotels, and refer the nearest station near to your destination.

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Paris bus service also a good way of traveling and there are special busses available for most of the popular attractions.
Trains are a punctual, and comfortable way to travel and connecting Paris districts and the some of the European countries. The TGV (Train a Grande Vitesse) is popular among the tourists.

Visitors can enjoy boat rides through the Seine River. Not only you can get a good time, its alternate to city traffic.

Most of the tourists are used to rent a bicycle and travel also. This is a good alternate to city traffic. You can rent a bicycle from most of the train stations and bicycle rote maps also available. Tour de France, the famous bicycle race takes place in every July.
Car renting is not recommended because the intense traffic and the shortage of parking place. You may need to obtain an international driving license also. Illegally parked cars will be towed away by authorities. Walking also a good and enjoying option.

Useful Links
Paris Train Stations: Clik below links for Paris Train station information from paris.org
Gare d'Austerlitz
Gare de l'Est
Gare de Lyon
Gare Montparnasse
Gare du Nord
Gare Saint Lazare

Paris Metro Information:
Paris Travel