Arunachal Pradesh State Transit APST does run some government bus service, however they operate mostly in the plains area and are often infrequent and unreliable. The timetable on the APST website lists services that do not exist and should not be relied upon when planning your trip.
The main mode of transport is shared Sumo taxi. These taxis operate a private network between villages in the same sector. Sumos carry 10 sometimes more people and generally leave each morning around 5.30 am check with the Sumo counters the night before to be sure.
It should be noted that the road network in Arunachchal is not overly developed and it is often not possible to move directly between one village or another. You will often have to return to the plains Itanagar, Pasighat or even Tezpur Assam instead of going directly from town to town.