Here are the recommendations I gave when I took groups to France. Whilst they may not all apply to your personal circumstances, you may find some of them useful:
If you know no French, learn a few basic greetings and use them continually and wherever you go. That even includes saying "bonjour" and "merci" to the person who sells you entry tickets to an attraction, when you enter a restaurant, or you ask the Mac Donald's attendant for a Big Mac.
Keep a low profile and speak in moderate tones. Do not exclaim loudly about things or comment about them in a critical fashion because they are different to what you are accustomed.
Do not accost people you do not know except in a tactful manner to ask for directions, or engage an unknown fellow traveller in conversation and tell him all about yourself, why you are in France, when you arrived and propose to leave. Likewise don't give strangers your life history or long descriptions of your family or of where you live. Keep that for the people you know and only if they ask you questions about yourself.
Do not ask personal or indiscreet questions. It is not done. Never discuss your bodily functions or illnesses except with a doctor.
Do not go to a person and say "Ho, my! I do love your shoes. Where did you buy them and how much did they cost?"
Do not be over familiar with waiters or waitresses and do not be offended if they do not engage you in chat. They are respecting your privacy.
Respect the places you are visiting and do not leave litter, sweet wrappers, tissues, drinks cans and the like in public places: use the bins provided in the streets. Most of the litter on Paris pavements is cast away by tourists.
If you want to be inconspicuous avoid over flashy clothes for everyday wear, or too garish colours.
On the other hand do not go around town in sportswear or sweats, or tatty holed jeans and distressed clothing . Girls should avoid wearing micro shorts in an inland town (seaside is OK) and never when going into a church.
Be patient, respect queues and do not overtake others unless you have a pre-bought ticket.
In shops do not handle goods unless you intend to buy them, try hats for fun, disarrange a neat pile of clothing and just throw it all back.
Be punctual for meals if you are a guest, or if you have booked a table at a restaurant do not arrive two hours late. If you are delayed, phone.
If you are invited to eat somewhere always take a small present. It does not need to be expensive if you are on a small budget; it is just a token of appreciation.
Mind your table manners. When a guest, wait till the lady of the house tells you where to sit then either tells you to start eating or starts herself. Do not overload your plate when food is passed round for you to help yourself, and think others have to be served after you.
Whether you are eating in a restaurant or in a private home, do not pick things up from your plate with your fingers. Use the napkin provided and wipe your mouth before you drink from your glass. Do not leave the table throughout the meal. If you need a bathroom call, go before or after the meal.
Do not smoke in public places- or in people's home without their consent.
If you are over 18 drink alcohol in moderation and do not get drunk.
Put your hand in front of your mouth before coughing. Do not chew and talk at the same time, particularly if chewing gum.
Do not walk around town eating food (except for ice-creams). It you have sandwiches, sit on a bench or in a park and dispose of wrappers in the bins provided.
When in somebody's house never wander out of public rooms without the owners' consent, and do not poke your nose into bedrooms: they are private territory.
In smart hotels do not leave the room littered with dirty underwear or discarded clothing all over the place before going down to dinner: there may be a turn down service and the maid who does it will feel obliged to tidy up for you, which reflects badly on you and could be embarrassing for you too.
If you spot fellow countrymen whilst in a hotel dining room, do not shout across to them "Hi! I am American too. Where are you from? How long have you been here? What did you do today? What did you think of .....?" Wait till they or you have finished your meal and have moved on to the lounge for coffee or drinks to accost them.
When walking alone, do not grin at strangers: people will wonder why you are doing it and if you have a 'bizarre' agenda.
These are basics and some of them may already be routine for you, but believe me some people can really behave like morons when they are abroad and take liberties which are absolutely shocking.
Basically if you think of others, do not invade their personal space, are polite and courteous and keep a low profile, you will have no problems.
Have a great time!