When a food photograph makes you hungry, there's a good chance the food looks juicy. Think of a photo of an apple and then think of a photo of that apple just after being cut and the juice is dripping down the knife and skin.
To make sure you get the most shine in your photo—get your main light (whether sunlight or bulb) coming from the side or back. What your essentially doing is capturing the reflection of the light off the water or oil and bouncing it back directly into your lens. Too much can cause hot spots, so be sure to take a bunch, varying your angle slightly, to get just the right amount.