Hugs. Especially as a greeting.
While I've learned to faire la bise to my co-workers and my boss upon arriving at/leaving work, I still don't like it. I haven't even let Ma kiss me since elementary school, so you can imagine how uncomfortable it is for me to greet people here in France. I'd much rather receive a sincere bear hug than have someone's mouth that close to my face.
Smiling and/or talking to people in public without it being taken the wrong way.
This may seem contradictory to what I wrote the other day, but I actually do really like being able to smile at people I come across when out and about. Smiling at people you don't know is very useful, especially for folks like me who aren't big talkers. It eases tensions and levels the playing field when you're in awkward situations. It's also a wonderful icebreaker. But it's just not something French people (I mean Parisians) seem to do all that often. It's like you're supposed to walk around pretending that no one else is there. No direct eye contact, no facial expressions, and definitely no words. And that makes me feel kinda lonely sometimes.