The fastest education in local do's and don'ts comes from watching, not reading. Guides give you the headline rules, but real calibration happens by observing how locals behave in queues, on transport, at meals, and in offices, then quietly matching them. Give yourself permission to be a careful observer for your first few weeks rather than the loudest person in the room.
A few universal safe moves while you learn: err on the formal and polite side, ask before photographing people or religious places, keep voice volume moderate in public, respect queues religiously, and be careful with humor about religion, politics, and the country itself. Punctuality norms, tipping culture, shoe removal at homes, and greeting styles are the classic variables that differ country to country, so check those specifically for your destination.
The other shortcut is simply asking. A colleague or neighbor asked sincerely, what should I know so I do not accidentally offend anyone, will usually respond warmly and tell you things no guidebook mentions.