Carat Weight
How big do you want your diamond?
This is an obvious one. The bigger the carat, the more diamond you get. Carat is a unit of measurement used to weigh diamonds.
Clarity
How clean do you want your diamond?
Clarity refers to how much blemish or dings your diamond may have and how big those blemishes are. Each diamond is unique, and most diamonds have some flaws on them. Some diamonds have flaws that are visible with an eye, some only visible with a microscope, and the more rare ones, have no blemishes at all. The more flawless a diamond is, the more rare and expensive it is.
Cut
What shape do you want your diamond?
Cut describes the design of the diamond. It also describes how skillfully the diamond was cut to interact with light. The right cut will make your diamond sparkle bright like the stars!
color
How clear do you want your diamond?
Diamond color refers to how clear or colorless the diamond is. Even if the most subtle hint of color is detected in a diamond, it will change the quality and price of the diamond. The more colorless a diamond, the more rare it is. This picture from the GIA website shows a scale of how diamonds are graded.