Getting from Florenc Bus Station to Prague Airport
Florenc bus station
Autobusove nadrazi Praha Florenc (bus station Prague Florenc) is the main terminal for long distance buses connecting Prague with other European cities. It is where most international bus lines terminate in Prague and where you are most likely to end in case that you go to Prague by bus.
Prague International Airport in Ruzyne
Airport Praha Ruzyne (PRG) has grown into an important hub for flying between western and eastern part of Europe. As a result, the airport is used by people not only from Prague, but also from various regions in and outside the Czech Republic. If you fly from Prague International Airport and come to Prague by a bus, this is how you get from the bus station to the airport.
Taxi from Florenc bus station to the airport
Taxi is always an option. There is a taxi standpoint next to Florenc bus terminal. The price will probably be somewhere around CZK 500 (EUR 20).
Florenc to Ruzyne Airport with public transport
You can also use Prague public transport, which is less comfortable, but during the peak hours on a working day equally fast as the taxi. The price for a one way ticket is CZK 26 (about one euro).
From Florenc you take metro line B (yellow; the deeper one) two stops to Mustek, where you transfer to line A (green) in direction to Dejvicka. You go with the A up to the end station Dejvicka and in that station you look for signs leading to buses to the airport. The bus number is 119. Both metro lines and bus number 119 operate with short intervals during the whole day including weekends. The whole journey from Florenc to the airport takes about 45 minutes (and it is good to have a few minutes reserve just in case).
Between midnight and early morning you will have to take night buses: 504 from Florenc to I. P. Pavlova station and then 510 to the airport. Intervals are much longer with night buses (typically 30 minutes).
There is a bus signed AE, Airport Express, also operated by Prague public transport company. You can get on this bus at Dejvicka or Hlavni Nadrazi (Main train station). Though it has fewer stops than the 119, the eventual travel time difference is not significant.
Note that usual public transport tickets are not valid in the Airport Express and you will have to buy two separate tickets for the metro and the AE. One-way Airport Express ride from Dejvicka to the airport costs CZK 30, from Hlavni Nadrazi it is CZK 50.