Between the age of 12 and 24, if Jupiter is in the house of Venus and has Venus opposite to it, one could be sure that the native would have a relationship or marriage during this period.
If Saturn is being transited by Mars and its dispositor is placed 8th in any sign one cold be sure that there will be reversal in his or her professional career
If Saturn is in Taurus and the next planet is Ketu in Libra for example and there are no planets between Saturn and Ketu, it would show that a person would take a long time to settle down and instead struggle.
Ketu is the unknown portion of karma and the planet ruling the sign of Ketu is the incoming or past life, whereas Rahu controls the Karma distribution in this life
Yogas combination made by Ketu will make a person great, but will destroy him whereas combinations made by Rahu will make the native enjoy powers lifelong, till his death.
It will be seen that a debilitated Mars having Rahu ahead of it with no other planet in between and Moon 12th to Mars and if it is horoscope of a lady, it can be predicted that she will be deceived by a person which will have a great impact on her destiny.
Retrograde planets can mean many things, for example if one has a retrograde Jupiter it is indicative that the native was probably a drunkard in his past life, a very biased and prejudiced individual and this tendency would come in this life time too. This would be the inner trait and the character which would drive the native.
Retrograde planets in the house and sign placed will signify negativity and non fulfillment of matters related to that sign. On the other hand, if they are well aspected or have powerful planets in conjunction or on either side of them, it will energize these planets and give the person energy to work positively and scale greater heights.