5 basic methods of selections of precious stones.
The first method by the position of the Moon in the horoscope, (rasi). For example, if the Moon is in the sign of Leo. Leo is ruled by the Sun, the corresponding gem is ruby or other good red stones like garnet or red spinel.
The second method is based on the nakshatra under which the person was born. Each nakshatra (there are only 27 such constellations) is ruled by one of the nine planets. This stone is considered the stone of the star under which a person was born.
The third method is based on the ascending sign, (lagna). For example, the rising sign Leo is ruled by the Sun, respectively, the ruby stone.
The fourth choice of talisman gemstone is based on preference. If a person is attracted by the influence of a certain stone, provided that it is not a dangerous planetary stone (krura graha ratna) or does not affect the horoscope destructively (located in a place of a retrograde race or an enemy race or other malefic places), in this case a person can wear a stone, which he likes. This last point should also be taken into account when choosing stones for rasi, lagna and nakshatra.
The fifth and most accurate method is based on the advice of a qualified astrologer. First, an experienced astrologer will rectify the time of birth and study the location of the nine planets in a person's horoscope and determine which planets to strengthen more favorably. The same time of wearing stones can be prescribed according to mahadashi, the main astrological period, antardasi sub-period, along with other astrological conclusions. This last method is the most powerful method of selecting gems for the correct use of their power. Consultation with an experienced astrologer is very important.