Sometimes it is still very obvious I am a foreigner, even after all the years I've lived here. There are little things I do that I realize that I'm supposed to do a different way but I usually forget until after I've done them wrong.
Like in the U.S., at least in my neck of the woods, when you run into a friend or acquaintance at a store or restaurant you yell out "Hey!" or hi or hello. Where I'm from it's a "Hey y'all!" But here it's normal for people to yell out "Adios" when you are passing them. I told my husband that sometimes I feel like the Beatles song Hello Goodbye. "I don't know why you say goodbye, I say hello. Hello, hello."
I also always say "Hola" to people when the proper greeting is "Buenos dias or Buenas tardes or noches". I walk up to the door of the school to get my boys and automatically say Hola to the people around. I think I must sound like a little kid when I do that.
Another thing I never get right is showing sympathy. I'm good at showing it, but the words are always all wrong. I second guess myself how to say I'm sorry for your loss or for whatever is making you sad. I mostly just end up hugging the person. That usually seems to smooth over my lack of eloquence.
At least I've got the kiss down. I always go to the left for the hello and goodbye kiss. When I was a student in Guadalajara, I accidentally went to the right and got my host family's aunt right on the mouth! Thankfully that one time was enough to learn the right direction.