To get to Arica, Chile, take a colectivo taxi from the international terminal, located next to the domestic bus terminal. You will encounter many touts on the way between terminals, but you may wish to wait until inside the terminal to secure transport as prices vary slightly. "Official" colectivos are reachable through the gate marked "Taxi colectivo" and their price is clearly marked on a sign: as of September 2014, you have to pay 1 sol for the terminal departure tax and 18 soles (or 4,000 Chilean pesos) per person for the colectivo. Although you will no doubt be assured that the colectivo is leaving right away, this is often not the case as they will not leave until full (if you are in a group of 4 or more you may wish to try and negotiate your own taxi). The driver will help you through customs and immigration. The journey takes between 1.5 and 2 hours, depending how long border formalities take: be aware that you are not allowed to bring animal and vegetable products (especially fresh fruits or plants) into Chile, so eat your remaining fruits before crossing the border. The colectivo will drop you at the international terminal in Arica; you can try and negotiate a ride to your accommodation but this may not be possible.
To continue onwards in Chile, walk to the domestic terminal right next to the international terminal and buy a bus ticket from there. Food, money exchange, baggage deposit and bathrooms are available inside.
Caretur Tacna (Cámara Regional de Turismo)