I love the flow of the juice in this picture and this would make for such a lovely picture if only it was executed right. The flash is really out of place and makes an ugly glare on the glass (That also brings out the dirtiness of the glass), the background is wrong, for such a commercial idea a white background would have been better. And the composition is too inyourface kind of, the subjects too close. You're on the right path but you're using the wrong shoes.
One thing that helps is direct overhead light, either you used a flash or a light source from the directiont he shot was taken - the reflection just kills the image.