Walking is not very popular for locals living in Guatemala City, and most tourists follow their example and use public transport. There are 3 types of buses that operate in Guatemala City: the Transmetro, Transurbano and red city buses. The Transmetro and Transurbano are modern and efficient, running fixed routes regularly. The drivers don't carry any cash on them and tickets must be purchased before you ride. The city buses, however, do accept cash payments on the bus and will make stops anywhere along the route – just shout when you're ready to get off.
The weather in Guatemala City stays relatively constant all year, with temperatures ranging between an average of 17°C (63°F) in January and 21°C (70°F) in April. June until September can be overcast and cloudy, and rainfall frequent, so if you're looking to avoid the rains on your trip to Guatemala City, plan to in the drier season!