There are two main kinds of public buses running around the city: the government operated RTP and the Microbuses.
RTP buses charge a standard $2 fare (no change, so pay an exact amount) for a journey of any length along their designated route. They are large, comfortable, and are operated by drivers who adhere strictly to traffic rules, and so these buses are a safer means of travelling.
The microbuses, or "peseros", on the other hand, are privately owned and operated, with drivers who are a little less mindful of the watchful eye of the law, and so present the likes of a roller coaster ride for around 3 to 5 pesos. These buses have a smaller seating capacity and are usually crowded, with passengers clinging to the doors, so be careful while using them during peak hours. Microbuses operate from 5 in the morning to midnight.
The buses stop at particular locations only, so be sure you know which one to take before you get on.
The route for each bus is displayed on its front window, so make it a point to go through it if you are not sure the bus is taking you the right way.Another tip for bus travel in Mexico City: buses usually make abrupt and very brief stops, so be sure you know where to get off and you are prepared to do so when the bus stops. There is usually a push-button near the rear door that you can use to alert the driver that you want to get off.