The bob is a short hairstyle that is simple, but classic. Having a piecey bob style adds an edge to the typically sleek look. It also works very well with natural waves for an effortless haircut. Make sure hair is smooth with no frizz, because frizz is more evident in short styles.
The concave bob is an asymmetric hairstyle that has been seen on the likes of Victoria Beckham. This style is longer in the front and slightly shorter in the back, with many layers. The layers are much shorter at the top. Also, bangs look very good with this type of hair style. Side-swept bangs will have the biggest impact as they are asymmetric as well.
A long bob extends somewhere between the the chin and the shoulders. This style incorporates layers of many lengths. The longer bob allows for waves and other natural hairstyles to be used. A light spray gives the pieces texture and the hair volume. Straight hair works with bobs, as well, just make sure that you have lots of layers to achieve the piecey look. Pull back your hair on the sides using barrettes for a different look.
Short, piecey bobs give you an edgy look. While they do not have to be as asymmetric and short as the concave bob, they can still be edgy, with thick layers. The shorter layers on the bottom give your hair more volume, however, be careful of having too much volume with short bobs, because this will create a very rounded look. You can make your bob look cute and classic with headbands or by tying a ribbon in your hair.
References and ResourcesBella Online: Layered Chin Length Bob and Variations
Beauty and the Bath: Concave Bob Hairstyle
InStyle: Top 10 Haircuts and Colors Right Now