The French tend to be a lot more formal with their attire than American's are. Shorts for sight seeing are okay but only if they are not too short. If you are going to a restaurant or museum you'll want to wear pants or a dress.
The first thing on every tourists list is to see the view from the top of the Eiffel Tower but there are some other must see stops that you might find even more breathtaking like the view from the top of Notre Dame and Arc de Triomphe.
Les Cars Air France is a bus service that you'll find much cheaper than any taxi when you arrive at the airport.
If you can't speak French fluently then don't speak it at all. The french tend to get offended when tourist "butcher" their language.
Most museums are open late at night. This is the best time to go to beat the crowds.