Only in Paris for about 2-4 days in July

You can see twice as much in 4 days as you can in 2 days, so what you fit in depends on how much time you end up having available.
This is my Paris 'Top Ten' for first timers ...
Arc de Troimphe+Champs Elysess
Notre Dame
Pompidou Centre
Eiffel Tower
Musee d'Orsay
Sacre Coeur+Montmartre
St Chapelle+Conciergerie
Louvre
Place des Vosges+Marais
Versailles

I wouldwalk everywhere. Eiffel tower, along the seine, to notre dame cathedral, down the champs elysee, and to 1 park ie luxumbourg garden, montmarte for sacre coeur church. Leave museums for another time unless it is raining. Enjoy and have cafe creme and croissant at a sidewalk cafe every morning a must. Lucky you.

If you don't already have a good guidebook, get one and study it. Determine which sights are the most interestibg to you and prioritize them. You will get more out of your Paris adventure if you visit the places most important to you than if you are trying to see everything and checking the sights off a list. Of course, 4 days are better than 2. Planning is part if the trip, so plan well and enjoy.

Check out a guidebook or google "Paris 10 best" sights and then see what appeals to you. We don't know what you're interested in, it's up to you to determine what you'd like to spend your time and money doing. Same for London on the other thread.

When will you know whether you have two days or four days in Paris? Four days is probably more than a lot of people get to spend there and can make a difference in the kind of advice you get from us. As others have said, a guide book is essential so start with that.

As the others have said, there's a big difference between two days and four. There's also a big difference in what we would put on our individual must-see lists so only you can make that decision. For instance, was Louvre and a shutter-bug session in Père Lachaise were high on the gotta-do list for me but going up the Eiffel was not (and I didn't: got a great eyeful from the Trocadero at night). Get guidebook, make a list, and then prioritize it so your top choices are sure to get done.

Soccergirl, as you can see the more info you provide the more detailed info you can get. Like when are you going to Paris, Summer, Fall, Winter, or Spring? This info can help with your "dress" attire. Looking up the weather for your timeframe from last year can give you a heads up on what to possibly expect, www.wunderground.com. Comfortable shoes is always a must, especially if you plan on doing a lot of sightseeing. If you are into the nightlife scene of night clubs and or 4 & 5 star restaurants then you would wear the same attire that you do at home. Do know that there are plenty of restaurants, Bistro's & Cafe's that serve good food that do not require formal attire.

With only 2 or 4 days I would skip Versailles. Save it for a future trip with more time. I would definitely see the Arc de Troimphe & Champs Elysess, Notre Dame, Eiffel Tower, Musee d'Orsay, Sacre Cour & Montmartre, St Chapelle, the Louvre & Luxembourg Gardens. As far as what to wear, be comfortable especially your shoes. You will be doing a lot of walking. Dress up if you like to go out for dinner (or not your choice really) but more casual in the daytime is fine. Enjoy your trip!