Create layers. Layering hair creates an illusion in two ways. The first is that is creates of illusion of length with the long hair. An illusion of volume is created by the short hair. Hair layering can be obvious, but some can be blended in looking more nature and softer.
Another way to make layers obvious is to color the layers. A popular layering color is black and blonde or black and red. Many celebrities are known for the layers in their hair such as Selena Gomez, Kim Kardashian, and Tariji P. Henson.