The Mexico City Metro is one of the cheapest, fastest, and most extensive in the world — 12 lines, around 200 stations, a flat 5 peso fare (about 25 US cents). It runs 5 am to midnight on weekdays, and you can get from the airport to the centre in 40 minutes. The trains are jammed at rush hour and the system can be confusing at first; download a metro map and the Citymapper app before you arrive. Pickpocketing happens; keep your wallet in a zipped pocket.
The Metrobús — articulated buses on dedicated lanes — fills the gaps the Metro doesn't reach, including the full length of Reforma and Insurgentes. The same Smart Card works on both. Taxis are everywhere but use Uber or Didi for safety and price clarity. Driving yourself is not recommended — the traffic is brutal, parking is hard, and Mexican drivers operate on different rules from anywhere else. Cycling is risky but improving; Ecobici, the city bike-share scheme, covers Roma, Condesa, and most of the central area.
For altitude: 2,240 metres affects nearly everyone for the first day or two. Drink water constantly, avoid heavy alcohol the first night, and walk slowly.