Unless you plan on going to one or two museums in Paris, you may want to consider a Paris Museum Pass.  This will allow you to bypass all the ticket lines and go straight to the entrance (there may be a line to get in of course).  We ordered ours ahead of time and had it mailed to us.  You purchase the pass by the amount of days you want to use it – 2, 4 or 6 consecutive days.  Once you activate it (put the first date of use on the back) Paris becomes your oyster.  The Louvre is so massive, having the pass allows you to go back and visit different wings on different days. The pass also covers monuments like the Arc de Triomphe, Notre Dame, Saint-Chapelle, and many others. Passes doesn’t work at the Eiffel Tower so bring money! For the big, main attractions, try to get there as early as possible to avoid crowds and to allow time to see more sights per day. Enjoy!