What should I know before going to Paris?

NOT EVERYONE SPEAKS ENGLISH

always ask First assuming they do speak English is Insulting

First thing to know is some French!  Food is noted for being good, but Lyons has better.  Versailles is worth the visit.  Don't expect to see the Bastille==it was torn down during an uprising in 1830.  Moulin Rouge is a bit of a tourist trap, but worth seeing anyway, as is the Pompidou Centre.  If the Eiffel Tower is your taste, do go.

I would love to know what Marie means by 'butting out on the streets'.  In Britain I really cannot think what that means.

A few words of French. We don't expect you to be fluent, but at least bonjour, merci, 

s'il vous plait, parlez-vous anglais, au revoir.. And hopefully not with a snobby accent.

Rest is difficult to know without knowing your interests/what time of year you're going.

Fromage Gateau is not Cheesecake . It is a cake of cheese. Oh, and from experience don't drink the tapwater in paris. It would be insane or rather the Seine would be in you.

It's a marvellous place to visit, but it's good to know the etiquette when entering and leaving shops and other places of business. When you walk in, you always greet the first employee you see there with a 'Bonjour Madame' for a woman and 'Bonjour Monsieur' for a man, this is basically hello sir, or hello ma'am. And when you leave, you say 'Merci et au revior, madame/ monsieur' which is basically thank you and goodbye, sir/ma'am. Not doing it is considered a bit rude, and also marks you out as a tourist.

It's also a good idea to learn a couple of basic phrases in French, like Hello, goodbye, please, thank you, Do you speak English? Nobody expects you to be fluent, but you are going to a country with a different language, so it's more of a courtesy on your part, and it can really help open doors. Most of the people there already speak English anyway, it's part of the job description when dealing with tourists.

And the last thing: Europeans generally tend to be a little bit more reserved until they know you. They're not going to be all 'HIIII!!!' and your new best friends. You are a customer, they are as courteous as they need to be to you. They'll help you with whatever you need, but that's it - until and unless they warm to you. Stay friendly, pleasant and bring your sense of humour and an open mind, and you'll help yourself more than you know.

Make time to eat at PAPA Joe's just a short 1/2 mile walk west of the leaning tower of PISA 

What do you mean, mixed reviews? People who have never been there have posted some negative things, based solely on their dislike for Muslims. Paris is a magical place. I have friends who were there during the recent transportation strike. They had to do a lot of walking, but otherwise had a great time. Paris is a city for walking anyway. What Marie has told you is about money. It's true that there are some high-priced restaurants and bars that cater mostly to tourists. But you walk around and find very good places to eat everywhere. Go in one of the many small markets with produce stands outside, or to one of the outdoor markets, buy some bread, cheese and wine, or a sandwich or pizza slice and go to a park to eat. Take the boat ride down the Seine from the foot of the Eiffel Tower in the evening, about a half hour before sunset. It's less crowded then, and you'll come back up the Seine in time to see the tower light up. 

What do you want to know?

It's a great city to visit; as with every major city, it's busy, and it can be overwhelming. Some people love it, some people don't.

Learn to speech French.