Someone like me who grew up in Sweden probably looks like the biggest introvert to Americans, but the Swedish norms are just so ingrained in me at this point. When I came to America I only greeted people if they greeted me, I usually look at the ground to avoid eye contact. Something that is common for Swedish people to say about Americans and one of the big problems for us is that it seems like you have a lot of friends but no close friends. Friends in Sweden are usually your closest friends that you interact with on a day to day bases, and little to no interaction with random people happens. For someone who is coming to America for the first time get ready for a lot of nice people who will have a friendly greeting, but be careful because most of them do not actually want to engage in conversations.
I always had a hard time with people asking me "what's up?" I started to engage in conversation when they really just wanted you to say "good, how about you?". People that great you do not always want to start a conversation which is very different from Sweden, only time someone would say something is when they wanted to talk to you.