One Full day in Paris

Musée d’Orsay and Jardin Luxembourg.

I'd second the above, but if you are there off season or in winter, I would overdo the museums and say 'D'Orsay and Louvre'.

I’ll just add a nighttime itinerary thought. The Eiffel Tower after dark! You can just hop off the metro and walk up the street to it. It was magical. My favorite pictures and Paris memories this past January were walking by the Eiffel Tower. You don’t even have to try and go up since you may be in a time crunch. There is a fence surrounding it now but you can see it clearly and walk up close. Eiffel Tower was so pretty with all of the lights and stars in the sky after dark! Be very aware on the metro with your belongings for pickpockets- not to scare- just a word of wisdom.

Ok well I’ll offer a few other things we did that were so much fun- wander the neighborhoods in Montmartre and Les Marais. Get a crepe from a stand. Visit the Museum d’orsay- Get tix ahead of time so you aren’t standing in line forever or worse, not able to enter. Wander through the areas around and see the exterior of the magnificent lady Notre Dame- Ile’ de cite and ile’ St. Louis (sorry if I had a misspelling there)
I always like to try to create a photo scavenger hunt while I’m wandering- like doors- door knockers, shoes in windows etc. it makes the wandering so much more fun! Paris is wonderful- one day isn’t enough but I’m so happy for you even if you get to go there for a single day! I’m sure other travelers will have lots of other suggestions too but these were things my friend and I did and we loved it! Cheers!

Only one day in Paris? That would be so disheartening! I would visit L’Orangerie,
Tulleries and Musee d’Orsay.

I should add too- do a little research ahead of time so that you are wandering in areas that are historical and beautiful. Paris is a big city!

Thank you all so much. We are going to southern France for 10 full days and are considering skipping Paris for such a short stay (2 nights) and heading down to Avignon for two additional full days there. We may make Paris in another trip so we can get a full taste of Paris. I am thinking we would not have enough time to learn how to get around. More trips in our future.

Jeanie,
I don't think you can lose with either plan.
If you have 2 nights in Paris, one full day, you can have a terrific day. I would recommend not over planning the day.
IMO there are 2 main things in Paris: 1. the museums 2. the vibe.

Depending on your interests I would suggest one museum and the rest soaking up the vibe.

I have spent 14 days in Paris. I will be going back in May with my son (his first visit). We have 2 days. My plans are:
Day 1: Bakery stop.
Sainte-Chappelle and Conciergerie in the morning
Parisian cafe lunch
Walk the 7th in the afternoon
Nice dinner
Maybe the Montparnasse tower after dark
Day 2: Louvre at 9 am
Lunch in the Marais
Walk the Marais in the afternoon
Walk the Latin Quarter
Dinner

If I only had one day I would pick one of the museums and 2 neighborhoods.

Have a great trip!

Vandabrud clearly has a good plan and clearly has a lot more energy than me. And he knows his way around Paris after previous longer visits. I love Paris but I suggest putting that time into the part of France where you'll already be -- Avignon or elsewhere. Paris deserves a much longer visit, and fortunately you'll have time to do that in the future.

Thank you all for your suggestions. We are planning to return to Paris and will go to Avignon. Hoping the strikes will be minimal toward the middle of May.