Hi uhsreedhara,
According to your horoscope you are Aquarius ascendant ruled by Saturn. You are born in the Uttara Phalguni nakshatra ruled by Sun. Currenlty you are undergoing through Rahu Mahadasha which would be operational till 28/01/2016.
Sun rules a maraka house (7th house). So avoid Ruby. Jupiter rules the 2nd and 11th house, but is an enemy of the ascendant lord Saturn. So avoid Yellow Sapphire.
Venus rules 4th house of home, conveyances, etc. and 9th house of luck, fortune, spirituality, etc. and hence is a yoga-karaka in your horoscope. You should give strength to Venus by wearing its gem Diamond / White Sapphire / White Zircon / White Topaz in Silver / Platinum in the Ring finger of Right hand. It should be worn on a Friday of a shukla paksha in the hora of Venus.
For Rahu Mahadasha you may wear a Natural Hessonite (Gomed) in Silver (as pendant) touching the thymus gland area. It should be worn on a Saturday of shukla paksha in the hora of Saturn.
Thank You