Many smaller businesses close during the afternoon siesta hours (2-5 p.m.), especially in smaller towns and villages, not so much in the tourist areas and during high season. This is also quiet time, so you’re expected to conduct yourself in a befitting manner. The upside to this is that shops and essential businesses like pharmacies will re-open after siesta and often stay open very late, so for any emergency, you can have an appointment up until roughly 8 p.m.
Sunday closures are also very common, except in very touristy areas.
When visiting religious sites, dress modestly by covering shoulders and knees. It’s also customary to remove hats before entering churches. Respect local traditions, and you’ll be warmly welcomed by the locals.
Greeks by nature are expressive and as well as being loud when speaking, they gesticulate a lot–using their hands when talking and often hugging their friends, sometimes people they’ve just been introduced to. If you feel uncomfortable with such close proximity too early on in an interaction, be the one to lead and extend your hand for a handshake with a smile. You won’t offend.