There are many factors that determine the quality of a diamond such as its cut, clarity, color, etc. However, finding a gemstone that meets all these diamond qualities will be challenging, and if found, such diamond rings will be very expensive.
It will be wise to look for the factors that reduce diamond ring values rather than the factors that complement it. This will save you from spending thousands of dollars on a low-quality diamond ring. One of the main things that lower the quality of a diamond is the inclusions in it such as black dots, crystals, lines, feathers, etc.
Usually, best quality diamond rings will be flawless and expensive. In case you are on a budget, you may choose a diamond that does not have any internal flaws when viewed with naked eyes. You must also be very attentive to check whether there are any chips or nicks on the diamonds in your ring. If so, there is no point in spending a huge amount of money on it.
Note that, some nicks will be microscopic and will not hugely affect the value of a diamond. That is, bigger and numerous the surface flaws, less the diamond ring values. This is because the probability of a chipped diamond to break is more when it gets hit on the same place.