Acupuncture works by inserting needles into specific points along Meridians to effect a change in the Qi flowing within that channel. There are basically two main techniques used in acupuncture: Tonification and Sedation. There are various ways of utilizing these techniques while giving an acupuncture treatment, some of them are more clinically effective than others.
For example, inserting a needle upon a patient's inhalation or during a patient's exhalation, whether you insert a needle along with the flow of Qi direction within a meridian or against the flow, whether you twirl or spin the needle in a clockwise or counter-clockwise direction will have either a more tonifying or sedating effect.
The length of time the needles are left in will have an effect on the Qi, the longer the needles are left in the more sedating the effect, even while giving a tonifying treatment. The amount of stimulation will also vary the effect on the Qi. It is also believed that different materials used to make the needle will have a different effects on the Qi.