Shaking your chest, it's about a sense of straight power in your lower body, as long as your chest is shaking.
Twisting the waist, first learn to twist your hips, use your hips to drive the waist, so that the coordination will look good.
To the mirror more practice exercises, in fact, very simple.
It is recommended that you go to find some videos about belly dance to see.
The movements in it should help you well.