ACV is extremely acidic. So I would not take it on empty stomach. I would take it after eating a meal. Like 2 tbsp in a glass of water. That way it will help with digestion of food.
Alternativly, u can take freshly squeezed lemon in a glass of water after eating your food.
The extra acid will help with digestion.
Taking ACV on empty stomach may make your stomach hurt, because u just reduced the acidity of the stomach, when it was not needed.