Santiago will be your main problem, the little signs there are, are located in places where you see them only too late and you missed your turn. Its a Dominican thing. Be careful when you ask for directions because most Dominicans do not know how to give directions and tell you want you want to hear. Sorry if I am generalizing but I have experience getting lost in Santiago, it can be frustrating.
Follow signs to Santiago basically the main highway. When you are approaching Santiago a couple miles after the big hotel and hospital under construction on the right side, stay in the right lane because the road will split and THEN it tells you the sign to Puerto Plata, once you are already on the road. Then you basically stay on this road, stay on the elevated section through town, go straight through the roundabout at Ochoa Motors continue on toward Navarete and turn off (this one is marked good) to Puerto Plata. You go on this mountain road for about 45 km or 30 miles and after you pass the RIU hotels in Maimon about 3 or 5 minutes later you will see some signs including a big one for Ocean World, thats the entrance to Cofresi which splits into two - take the left one and Sun Village will be on the right side big hotel you can't miss it. If you end up in Puerto Plata you missed the turn off.
The whole trip should take you about 3.5 hours if you are coming from Las Americas Airport Santo Domingo.
I hope this helps. When you do ask for directions, ask another person right away you will see how funny it is people tell you different way every time you ask.