Use common sense - if you have it. Keep your expensive stuff at home. Don't give your passport to anyone. Don't rent a car if you don't know the roads and driving conditions. If you must take a motoconcho, stay only on local streets. Don't ever take one on the main roads from town to town.
Don't carry any more money than you need for the time you'll be out. If you have time, get a prepaid card or a bank card not attached to any of your other accounts, and pull money from there.
Stay away from drugs, kids, tigres, and expats who want to tell you what "experts" they are on everything - oh, and can you spot them a beer?
Expect to pay a bit more than back home - you're on vacation, stuff happens.
Drink twice as much (bottled) water as anything else you have. It's a hot climate, and dehydration is real.
You're going to Sosua, which means you'll probably be looking for chicas. Use protection EACH AND EVERY TIME, and agree to a price up front. Do NOT get into fights over money, you will always lose.
That said, there's a whole lot more to do on the North Coast than monger. Get out, explore. Do some excursions. It's a big, beautiful country.
If it sounds too good to be true, it probably is.
If you're gonna drink, keep it with you at all times, unless you're with someone that you trust implicitly (spouse who actually likes you, ride-or-die friend, etc.) That goes for men and women.
If you spend your entire trip trying to save two pennies and keep from getting "scammed," you will have a miserable time.
Established restaurants MAY cook with filtered water. I'd check first before ordering anything raw (like a salad). Anything you get from a stand or shack that's rinsed should be fully cooked.
Keep in mind that the exchange rate is about 50 pesos to the US dollar. If you find yourself arguing over two hundred pesos for an hour, you just valued your VACATION time at $4/hr. It ain't that serious, and you should really consider letting the piddly stuff go.