Gems help to improve the bad effects of planets have on us. In general, gemstones should be worn to strengthen weak planets as calculated by the astrological chart. It is best to strengthen benefic planets when they are weak. Care should be taken when attempting to strengthen naturally malefic planets, such as Saturn, Rahu and Ketu, and gems used for this purpose should definitely be prescribed by a qualified astrologer.
Acharya Pankaj Kumar knows very well which gemstone suite to anyone. He does very well in the field if gemology to diminish the bad affects of planets and to increase the power of benefic plants.