Your coat length should be proportional to your height. This means if you are petite, you should seek out a coat of a shorter length. If you wear what everyone else wears, you will likely overwhelm your small frame. This makes you look wider as opposed to as sleek as possible.
You also should be cognizant of what you usually tend to wear underneath your coat. If you wear dresses or skirts to work, you should be able to see about 2 inches of your skirt below the bottom hem of your coat. Many people may disagree with this recommendation, but it is just my preference because if you can’t see anything under your coat, you may run the risk of looking like a street walker. I have nothing against street walkers, I just prefer the classy and timeless look of layering that you can see.
For additional tips on how to buy the right coat for you, see my previous post, Buy the Right Winter Coat.