How to structure your time, whether you have 2 days or 2 weeks.
Focus on the Old City in the morning (Grand Palace, Wat Pho) before the heat builds, cross the river for Wat Arun at sunset, then spend the second day between Chatuchak Market and a Sukhumvit rooftop bar.
Add a full day trip to Ayutthaya, a slower Chinatown evening for street food, and time to actually sit still in a riverside hotel rather than rushing between sights.
Pair a week in the city with a few days on the coast or in the north — Bangkok works well as a bookend to a longer Thailand trip rather than the whole itinerary.