Paris - initial thoughts ...
If you're heading out this way, get a travel pass from the tourist information desk at the airport before you leave. It covers you for all your buses, trains and metro travels around the city - make sure you get the right zones covered. Stock up on water locally before you head out for the day. 23cents local or around 2 Euros in the street of Paris central.
I used www.homestaybooking.com to find a room with a family. Basically you get a cheaper room than a hotel and local knowledge.
You'll get the usual hawkers around all of the sites of interest, particularly the Eiffel Tower. Don't be afraid to ignore them and keep on walking.
A lot of the eating places have free WiFi, so you can catch up on messages while you eat.
Don't forget to pick up a travel map with your ticket. If you've used the London underground, you'll be fine with the Metro.