For a round face choose a style with a short fringe, which lengthens the face and a short cut which makes the face look thinner. Round faces can add a bit of volume to the top of the head to slim down. Avoid spiky and short topside styling to your hair and any haircut that gives width or volumizes the sides of your face.
For those with long face choose a style with short layers or go for a bon with fringe which will create horizontal lines. Scrunch dried or curly bobs balance a long face. Long faces can layer it on for fullness on sides. Such faces must avoid short cuts, jaw-length bobs, or styles that add height on top.