For places:

'in' with general areas, countries, cities etc. = "I will arrive in Italy", "I will arrive in Rome"

'at' with specific places = "I will arrive at your house", "I will arrive at the airport"

You can use also use 'in' with a specific place if you mean specifically inside.
"I will meet you at the shop", could be waiting outside - but "I will meet you in the shop" means I will be inside.