The invisible bubble
Every culture has norms about personal space and physical contact. Latin American, Middle Eastern, and Southern European cultures tend to stand closer and touch more. Northern European and East Asian cultures generally prefer more distance.
Reading the signals
Mismatched space norms cause subtle discomfort — one person advancing, the other retreating. Watch the other person's comfort level and adjust. When in doubt, give a bit more space.
Touch and gestures
Handshakes, hugs, and back-pats carry different weight by culture and gender. Some gestures common in one country are offensive in another. Observe first, and let locals set the pace for physical contact.