There are multiple factors when it comes to choosing the perfect diamond. Every diamond is different and have different characteristics. There are 4 key aspects to mostly focus on which are; cut, clarity, color, carat.
This is of course in no order of importance, they are all equally important.
The cut of the diamond does not refer to the shape of the diamond, but rather the portions, symmetry and polish. The cut of the diamond determines how the ring will sparkle.
Clarity is based around how the diamond was created. There are "birthmarks" inside each diamond which are called inclusions. Clarity is rated based on the location of the inclusions.
Diamonds come in a variety of colors. The color of the white diamond determines the more true color it will reflect.
A diamond's carat weight is the measurement of how much a diamond weighs. A metric "carat" is defined as 200 milligrams. Each carat can be subdivided into 100 'points.' This allows very precise measurements to the hundredth decimal place.