Summarize the following:
The cut of a diamond will influence how the stone redirects light, causing it to glitter. Many consider this to be the most important feature of a diamond ring. Even an expensive diamond, if cut poorly, can look lackluster. The main categories of cut are:  Ideal cut (sometimes called "Excellent"), reflects the most light possible back to your eyes, making the diamond sparkle brightly. Very good cut, reflects slightly less light back to your eyes than an ideal cut. Good cut, reflects most of the light that enters the diamond back to your eyes. Fair cut, reflects noticeably less light than a good cut, but is generally considered to still be a quality gemstone. When a diamond seller talks about the color of a diamond, they're actually referring to its lack of color. Diamonds are rated on a scale that goes from D to Z. Diamonds that are perfectly white are the most desirable/expensive and are ranked at D.  Color grades can be minutely different from each other. Selecting a diamond with a unnoticeably lower color grade can save you a  significant amount of money. Ranks F to E will only have minimal traces of color that can only be detected by a professional gemologist. Ranks H to G are nearly colorless. The difference between these and higher color grade diamonds will only be noticeable when compared side by side. Ranks J to I will generally have a detectable warmth to their color tone, usually in the form of yellowness, but are still considered to be near colorless. Ranks worse than I will have noticeable yellow tones coloring the gem. Even the most expensive diamonds will likely have minute flaws and imperfections. Gem experts call these "inclusions." For high quality diamonds, these inclusions may only be visible with a microscope. However, too many flaws or the wrong kinds of flaws can make your diamond cloudy.  Clarity grades, from flawless to visible flawed, are rated: FL (flawless), IF (internally flawed), VVS1, VVS2 (very, very slightly included), VS1, VS2 (very slightly included), SI1, SI2 (slightly included), and I1 (included). You might save some money by choosing an SI1 clarity diamond. These often only have flaws visible under magnification, making them a more economical purchase without looking cheap. Before purchasing a diamond with a SI rank or worse, verify with the seller that the diamond is "eye clean." This means there are no imperfections visible to the naked eye. Small amounts of boron are frequently trapped in diamonds, causing a slightly milky appearance in the stone. This is called "florescence," and it is rated from Faint to Very Strong. Unless you are able to appraise a diamond in natural light to ensure there is no milkiness, you should avoid Strong or Very Strong florescent stones. Looking at your diamond from above will give you a better idea of how the stone will look when placed in a setting. While most people evaluate the size of a diamond by carat weight (CTW), this can be deceptive. Even small diamonds that have been cut correctly can appear sizable.  You'll also want to look at potential diamonds in many different kinds of lighting. Some stones look beautiful in bright light, but lose their appeal in everyday lighting. Carat total weight (CTW) is the weight of all the diamonds in the ring, including side stones. When only the CTW is listed, ask the diamond seller about the quality and weight of the centerpiece stone. If the seller does not want to share this information, this is likely a sign a sign that the diamond is low quality. The shape of your diamond will highlight different features. Round brilliant cuts will bring out the sparkle in your diamond. Step cut diamonds, like Asscher and emerald cuts, will reflect flashes of light as opposed to sparkle. Longer shapes, like oval, pear, and marquise cuts, can be suitable for longer fingers. Some other shapes for your consideration:  Round Princess Emerald Radiant Heart Cushion You'll want your diamond to have been graded by an independent authority so you know you're really getting what you're paying for. This is also known as a certificate, and will include an evaluation of cut, clarity, color, carat weight, light behavior, apart from providing other measurements such as fluorescence, proportions, alignment, symmetry, and fingerprint.  The GIA (Gemological Institute of America) and AGS (American Gem Society) are two of the diamond grading authorities in the US.  Beware of diamond grading scams: Diamond grades can differ from one lab to another, and also from one gemologist to another. This is due to certain shortfalls of the human eye, apart from other integrity issues. Note that the price of the diamond differs based on the diamond grade. There have been many diamond grading scams because of such subjective grading practices.

Summary:
Select a cut that maximizes sparkle and beauty. Equip yourself with knowledge about diamond color. Identify your ideal clarity. Take florescence into account. View potential diamonds from above. Pick the best shape for your diamond. Verify the diamond is certified.