Mexico City a great place. Listen to the folk and mariachi in the main plaza at night. Visit the museums, the cathedral, and enjoy the fine food. Need a jacket at night- can be cool, 18C or lower.
Lunch on major downtown streets from booths, clean and good, esp. the hot beef and pork sandwiches. Select by watching where the business people stop and order.
Google Mexico City's best restaurants. Stick to meat and fish, some of the offerings are not suited to our tastes.
Like all large American cities, stay out of dark streets and leave valuables in the hotel safe (or room in upscale hotels).

Odd places- Tapachula in western Chiapas. An isolated market city, but some good restaurants, clean. The plaza has a place near a corner making frozen drinks that are excellent. Take to their corner of the plaza and enjoy. High above the coast and close to it, but nothing developed yet. Excellent hotels. Mountains and coffee plantations.
Near the Guatemalan border.

Always drank beer in Mexico (esp. Dos Equis). Fruit juices in bottles or cans OK.
Caution- get it where they have refrigerated storage. Some small rural places put the bottles in a large cooler with ice. The ice water can be contaminated.