I recently completed a trip of 8 days to Paris and France. I used Rick Steve's travel guide for much of my planning. All of his information was quite helpful. What I have learned is the following:
1. Paris is crowded no matter what time of the year you travel. About 30 million visitors a year.
2. You will encounter scams on the street so be aware of these. I was approached with the "golden ring" scam on two occasions but thanks to the RS guide I was well prepared. I and a person I met were both approached by the take a survey scam where one person asks you questions while another takes your wallet.
3. The Metro and Carnets are the best way and most affordable way to get around Paris. You could also benefit from acquiring a good understanding of the buses. We could have benefited from the buses more. The biggest problem was leaving the Metro. Be sure where you are going out this was always the most confusing aspect for us.
4. The food in any restaurant will be excellent. I now understand why the French abhor American Businesses. You experience the many "small businesses or entrepreneurs" which is what US politicians constantly rant about. France has this but US corporations desire to manage this market.
5. You will walk in France so be in shape and be prepared.
6. A bit of french helps but we were able to survive quite well with our modicum of French language skills. We used 10 minutes a day Language Series by Kristine Kershul (with audio CDs)
7. Pin and chip cards work everyplace. Never had any problems at any metro, toll booth, gas station or restaurants.
8. Open a Capital One (Capital One 360) account as a debit card. This works very well. I transferred cash to my account before leaving and withdrew cash in Euros without any charges.
9. If you rent a car take the time to understand how to use a GPS. I did not rent one (20 Euros) a day but might have benefited from one. We rented from Hertz, a small diesel car and had no problems. Be sure you have a capable navigator to read maps. Back roads in Normandy are quite confusing but we survived. You pay for gas after pumping. France has a lot of toll roads but the Pin and Chip card worked at all times.
10. Go to Paris and France either in October/November or early spring. Paris gets 30 million visitors a year. And yes they all seem to go to the Louvre.
11. Museum pass is a great deal. Investigate Viatours. We used them for a bicycle ride through Versailles (great experience) and the Backstage Eiffel Tour (why would anyone stand in line for 10 hrs to go up Eiffel Tower when tours are not that expensive). We also had a lunch on the Seine that was not too expensive and was quite memorable especially when you see the Statue of Liberty on the Seine near the Eiffel Tower. I am always moved by this statue no matter where I see it. To me it represents the best and most promising aspects of America.
12. Take a hop-on/hop-off bus tour early in your trip to get your bearings.
13. To get from Charles De Gaulle we used the Roissy bus that costs 10 Euros per person and drops you at the Opera Garnier near Haussmann Blvd.
14. Streets in Paris are a mess. The names seem to change every block. I don't think the France every placed a street at a 90 degree angle. Streets come into a square at angles usually with 4 to 6 streets entering a square and street names are sometime hard to find.
15. All of the French are quite helpful. It was a good experience to travel that I should have done years ago.
Enjoy your trip but plan before going and it will be a great experience.
16. Google maps works very well for planning your trip and walking in Paris.
Use on-line forums such as these forums or Tripadviser.com. Bonn-voyage.