In South India Navamsa chart is a must for marriage. For example for Marriage one must look into the following :-

Placement of Karaka Venus (if spouse is female) and Jupiter (if spouse is male ) in Navamsa chart.
Placement of planets in the 7th house of Natal Chart and 7th Lord of Natal Chart in Navamsa.
Placement of planets in 7th house of Navamsa and 7th Lord of Navamsa in Navamsa chart .
The Lagna and Lagna lord of Navamsa. There should not be Malefics in Navamsa Lagna nor should Navamsa lagna have aspects of Malefics .The Navamsa Lagna Lord should not be afflicted by conjunction or aspect with Malefics or be posited in Trika house.
All planets should be well placed in Navamsa chart to make a early and successful marriage. This means the planets must be in exaltation sign or Own Sign or Vargottama or in Trine or Kendra houses. Also there should not be conjunction or aspect of Malefic Planets.
It may so happen that the 7th house planet will appear strong in Rashi chart but the marriage will pose problems. If the same planet is combust or debilitated in Navamsa ,it means it has no real strength and this is the reason for delay in Marriage or unhappy married life.
It is recommended that whichever planet is afflicted some small prayer and small Puja be performed to that planet after praying to Lord Ganesh remover of obstacles. One day fasting per week would be good if health permits. Consult a good priest .Be careful in selecting gem stones and consult an astrologer and don't consult jewellers who sell gem stones. The most challenging aspect in astrology is to predict the time when the event will happen. For this the Dasha / Antardasha and Transit of Planets will have to be looked and it is here the experience and acumen of the astrologer come into play. This is no easy task. For e.g. Venus antardasha under Rahu MahaDasha will give one result while you will get another result for Venus antardasha and Jupiter Mahadasa. Like these there are n number of combinations.

Author's Bio: 

Sri Tulasi is a professional astrologer having more than 15 years of experience.