Mexico City sits at high altitude in the centre of the country, and the two coasts are not interchangeable weekends off that capital. The Pacific and the Gulf/Caribbean sides have different water, different resort economies, and different flight connections. Colonial cities in the centre and the south (Oaxaca, Puebla, San Miguel, Mérida) are a third pattern. Spanish is the public language. English is common in beach hotels and thinner once you leave that strip.
The usual arrival is a long-haul flight into Mexico City, Cancún or Guadalajara. Airport-to-hotel is the first decision: official taxis, a booked car, or a ride-hail where it works. Intercity buses are the backbone for many routes; domestic flights cover the long diagonals. The country is large. A beach week and a city week are both reasonable. Doing both plus a ruin in the Yucatán as a single blur is how people remember airports.
Tap water is not what you drink in most places; bottled or filtered water is the habit. Altitude in Mexico City catches people who fly in and walk hard on day one. Cards work in cities and tourist zones; cash still matters in markets. The peso is the currency. A first trip holds if you pick a region and stay long enough to eat somewhere twice.
