Peak hours aren't really a thing in Paris (although expect more passengers between 7-9, 12-13, 17.30-18.30), moreso in July (quite a lot of tourists).
General travel in Paris advice :
My advice, for any long trip take the metro (don't go to the ticket machines if possible, got to the desks RATP agents tend to be really helpful as long as you're polite), depending the number of trips a day ticket or a 10 trips may be the best (if you're travelling in the same zone).Once again, the best is to ask the RATP agent on site and they'll get you the best deal. For the trip hotel/airport depending on where is your hotel the RER may be the best solution, taking the taxi is really expensive but may be more convenient.
In the metro/RER, like in any other big cities, be mindful of your possessions and read the mood. If everyone is shutting up, keeping to themselves and are blanked eyed, now is the time to not stand out and do the same. If everyone is lively and are chatting, there may be an event/concert etc.., ask around (politely) could be an opportunity to do something unexpected.
For short distances, get a good pair of comfortable shoes (and it will be a blessing whilst queuing).
If you need directions or tips (where is the closest cheap and cheerful eatery, etc...), start any interaction with "bonjour" during the day or "bonsoir" at night, even if you don't speak French. It's a standard and even if you are the nicest most polite person if the world, if you don't start a conversation by saying hello under French standard it will be considered extremely rude.
A simple "bonjour" and an awkward smile will often open you a lot of doors and get you around in a more efficient and cheaper way.
If you don't speak French, younger people (18-35) will tend to have a better grasp of English than older people. Otherwise it's like in any city, if you see him/her fast pacing, don't bother he/she is going to work/class etc...
If you are a person of colour, openly gay etc... be mindful that 23% of French people voted for the Rassemblement National in the European elections (extreme right generally racist/xenophobic conservative party). So some of my compatriots may not be as helpful as they can :/ , although most people are fine with you.
I'm painting a bad picture but in reality as long as you follow the Wheaton law, everything is going to be fine.
Have a fun trip and take the time to "boire l'apéro en térasse" !