First of all, consider the shape of the diamond and in case you are clueless about it then safely go for the princess cut round shaped diamond. Make sure your dealer weigh the diamond with an authentic carat machine because nothing is worse than presenting a half carat diamond to a woman. Check out the cuts and clarity before splurging your money for it.
Make sure your diamond has the right culet size and girdle because such details are very important to know to set the diamond in a metal surface as a ring. A perfect diamond also possesses nice polishing so the clarity, symmetry should be investigated before buying a real diamond. Don’t go for fluorescent as it is considered as a color defect to a natural diamond so sticking to colorless diamonds would be nicer.