Americans value their privacy, and as a result like to keep personal space around them. Standing within this space will cause an American to feel uncomfortable, and they will be more worried about how close you are than listening to what you have to say. How close is too close? Psychologists have found that most Americans prefer to keep a distance of 19 inches between people. That is about an arm's length distance. Make a conscious effort when you interact with Americans to keep enough distance so that if you reach out your arm, you will just touch the other person with the end of your finger.
 
Because of this space distance, physical touch is rarely appropriate for your initial interactions with Americans. A firm handshake when you meet someone is all the greeting that is normally considered to be socially acceptable. While in some countries it is quite acceptable to hold the hand of a person with whom you are talking, doing this in America is considered forward and often is understood to indicate a romantic interest. Don't make this mistake - It can be quite embarrassing!
 
On a similar note, Americans value cleanliness, and any form of body odor will hinder you as you seek to get to know Americans. Simply bathing daily and wearing deodorant will prevent you from having this obstacle to friendships with Americans.