Arica is a city in northern Chile, 18km from the border with Peru with many residents active on couchsurfing. The big hill next to Arica's city centre, known as the morro has a Jesus statue and a military museum with active people in uniform on duty. It's therefore not a good freecamping spot.
To Hitch south from Arica you can take a shared taxi colectivo (number 8) to "el agro" this is like a market on the edge of town. Ask the taxi driver to stop at the shell gas station. (You could also walk, it's about an hour from the center) From there all trafic is going far south. I waited less than 10 minutes for a ride directly to Iquique.
To go north, to Peru or lake Chungara, take a bus number 1 from center, last stop is off the city limits. Walk to the circle to get a good position to hitchhike.