A diamond face shape is very common. This shows a good example of what hairstyle suits diamond face shapes. The bangs help to shorten the length of our models face.
Old school slick back hairstyle
How to do the slick back hairstyle
Slick back wavy hairstyle
40 Slicked Back Hairstyles A Classy Style Made Simple + Guide
Just picture a diamond shape in your head.
There are lots of ways to decide.