Here is a list of sites that offer good tips when you're visiting Paris. I'll update as I find them.
Paris Voyage has a page with links with info on public transportation, Paris métro (the subway) RER (trains to various neighborhoods around Paris), bus, tram and Train system. It tells you how to read a map and where to buy tickets and passes and how to stay safe. Here is another good link for this type of information on how to move in and around Paris. Here is an article on taxis in Paris (hint, there is not such thing as hailing a cab in Paris. You go to cab station throughout the city.)