Are you driving there, or going by bus?
If driving, coming from Santiago, there's an exit from Autopista Duarte for La Vega/Jarabacoa. After exiting, make a right at the Texaco gas station and that's the road to Jarabacoa. If you're coming from Santo Domingo, you can take the first exit for La Vega and that puts you on Pedro A. Rivera Avenue, which is the old Autopista Duarte. Follow that for a few (6-8) kilometers through La Vega to the Texaco gas station which will be on your left, and make a left.
This belongs in travel directions, btw.