Bus No. 22 (Riga) takes you from the airport to the city centre.

Frequency 10 - 30 minutes, journey time to city centre about 30 minutes
A regular ticket for one trip can be bought from the bus driver 2.00 EUR, but if you buy it before commencing your trip at the airport services and tourism information bureau Welcome to Riga, in a ticket vending machine at the stop of Bus 22 and in Narvesen press kiosk at Level 1 and 2 of the terminal. Regular one-way ticket will cost you only 1.15 EUR.

Minibus No. 222
You can get from the airport to the city centre also with minibus.
 
The minibuses No.222 and No. 241 departs from P1 Parking. The minibuses depart every 10-15 minutes. The journey to the city centre will take around 30 minutes.
For the journey with minibuses No. 222 and 241 you can choose to pay:
with an e-ticket which can be purchased at the airport services and tourism information bureau Welcome to Riga”, Arrivals Sector E (price EUR 1,15) or at kiosks located in the terminal on the 1st and 2nd floor;
a single-journey ticket can be purchased from the minibus driver — price EUR 2,00;
Toll-free information line: +371 800 19 19

Taxi
Riga city and other destinations from the airport can be reached using SIA Baltic Taxi Lidosta or Panda Taxi
Journey time to the centre of Riga city is approximately 15 minutes.
Average cost per trip by taxi to Riga city centre: 11.38 EUR - 14.23 EUR