Never been there, but a good friend here at work is Parisian. Let me know if you want an insider's perspective on something, and I'll ask. Full disclosure, though: he prefers Houston to Paris, so maybe his opinion is suspect.
I've been to Paris multiple times, and I am not surprised. It's a great city for tourists - not so much to live in. My tips:
- Depending on how long you stay, get a metro-pass. They usually sell weekend passes and I think week-passes, which are always cheaper than buying a ticket for every individual trip. Driving in Paris is a nightmare, and the metro is super convenient, aside from the stairs at the Montmartre station, but there's always a lift
- Eat your breakfast in wherever it is you're staying. Go down to your nearest boulangerie at like 8am, get yourself a nice baguette - fresh from the oven - and pick up some cold cuts or cheese, milk and orange juice or a piece of fruit from a nearby convenience store. Unless your hotelprice has breakfast included with the price, but I've never stayed in a hotel in Paris, so I can't judge their food.
- Echoing HowDroll's recommendation for the Eiffel Tower at night. It's amazing. Or, if the weather is particularly nice, you can do it during the day and afterwards relax in the nearby park with an ice cream while sitting in the shade of a tree.
- Also echoing her recommendation for the Catacombs, but be prepared for a long walk, and do it in the morning, otherwise the heat when you come out will be overwhelming.
- The Louvre is, contrary to previous recommendations, easily done in a day, unless you're a superhuge art fan, in which case you'll be standing for hours in every single room. Also, the Mona Lisa is kind of disappointing. Huge crowd, tiny picture, so I was barely able to get a glance in. Again recommending to go in the early morning, you'll beat
most of the crowds.
Finally, I'd like to recommend my favourite restaurant in all of Paris:
Chartier. The food is simple and traditionally French, but the atmosphere is amazing and given the quality, it's probably one of the cheapest restaurants in Paris. It's also insanely busy once you get past 7pm, with waiting lines stretching all the way out of the alley and onto the street, so I recommend arriving at ~6pm or 6:30, unless you don't mind waiting. And if you do arrive to a waiting line, I heartily recommend toughing it out, because it's great. Tables for two usually go the fastest, though, so even if you do have to wait, it shouldn't be too long. I especially recommend the duck confit (confit de canard). Adress: 7 Rue du Faubourg, Montmartre. If you take the metro, it's the Grand Boulevards line, exit Blvd Montmartre. From there, it's just a minute walk to the nearest side-street (the Rue du Faubourg) and you should see an alley with a sign on your left hand side. Or just follow the line of people