To get to Jarabacoa from Puerto Plata, take Caribe Tour (it leaves every hour on the hour) to Santiago or La Vega (the stop after Santiago). You should be able to get a Caribe Tour bus from there to Jarabacoa. Caribe Tour has a bus terminal in Jarabacoa.
From Jarabacoa, you want to get to San Francisco de Macoris. To do so, you may first have to get to La Vega.If there isn't a bus, there will be a guagua. Same from La Vega to SF. In San Francisco de Macoris, you can get a Caribe Tour bus to Sanchez, the stop before Samana. Get out there and take one of the vehicles that meets the buses to see if there are people for Las Terrenas