Buy a five-day museum and monument pass (carte museés monuments) for your stay in Paris. It’ll save you a fortune in museum admissions and you won’t have to queue at the ticket office every time.
Buy Metro tickets in blocks of 10 (called un carnet): it’s considerably cheaper.
Try and make an effort to speak some French, even if it’s only “please” and “thank you”. It should get you a more sympathetic hearing. Almost everybody involved in tourist-related industries (including restaurants) speaks at least some English, but this is less common outside Paris.
As Gut pointed out, you’re likely to get further with British English terms than with US English. “Bathroom” for “toilet” is the obvious example, but I’m sure there are others (“gas” for “petrol”, for example). [By the way, do any American houses have an arrangement in which the lavatory is in a separate room from the bath? If so, what do you call is?]
Don’t expect Parisians to be any more polite than, say, New Yorkers.
You should strongly consider making a day trip to Versailles, which is very easy to reach from Paris by train and IIRC entry is covered by the museum pass. As with many of the state-run sites, you will be required to take a guided tour (available in English at no extra cost), rather than being left to wander round freely.
A decent three course meal with wine, if you have the set menu, can end up costing less than 150FF (~ $20), even in Paris. If you don’t have the set menu, a similar meal in the same restraurant could cost twice as much or more. Snacks and fast food can work out very expensive by comparison with the US.
The Michelin green guide to Paris is very good, as is the British Time Out Guide.
I’ll second Rocket’s nominations for Angers and Saumur. The latter has a mushroom museum which is worth seeing just for the novelty value and is actually more interesting than it sounds.
The Channel coast is swarming with Brits buying cheap fags and booze, but there are one or two nice spots, if you stay away from the main ferry ports.