If I were to say which forces of the horoscope are the most significant? I would say Rahu and Ketu, the North / South Nodes. These represent the desires of your current life. Rahu is the desires active and Ketu is those desires which are extinct! Indian astrology gives due respect to these 2 forces but western astrology refuses to even acknowledge them! But they are supremely important, e.g. a client comes to you for issues in buying a property, and you see the Rahu in 4thhouse, it’s a straight-forward conclusion that the fault is on his side, he tried to cheat, over-extend, be over-ambitious and has, as per Rahu’s indications, now fallen flat on his face. The direction of your desires is a very important indicator. You may have a beautifully placed Moon, Sun, Ascendant and everything else, but then your desires can pull you towards things which are not savoury or catastrophic for others and society.
Now these duo transit for long-ish periods too, spending 18 months, 1.5yrs in one sign. (The only planet which transits longer than these, is Saturn at 2.5yrs in one sign. Jupiter transits one sign in one year). Thus their influence is quite significant and sets the tone for these 18 months. So let us go through what can be expected from these two. As always the position from the ascendant is the physical/manifested context, the mental/emotional context is counted from the birth moon sign and the subtle aspects counted from the birth Rahu/Ketu signs.
Rahu is just the head, he has no body to do his actual work so he works through the planets he is placed with and the sign and the owner of the sign he is in. He will amplify over-extend and ultimately fall on his face in his typical Rahu style. A very simple example, a 5-yr old child with Rahu conjunct Moon will be extremely possessive of his mother all the time, won’t even let his dad kiss his mom, smother her with kisses, hugs and displays of affection, till 5-mins later he bangs his head on her nose attempting to kiss her some more, gives her a nose-bleed and gets a scolding himself. A baby Rahu over-reach!
Ketu has no head, he is just the body. Thus he indifferently accepts the influence of the planet he is with and the sign/owner he is placed in. He will give physical disconnection always, but will give a special astral/sub-conscious, almost dis-embodied awareness of these keywords. Eg, if the Ketu is with the ascendant, he will open widely the gates of the astral/sub-conscious/dreams/visions and the person will not even realize the dangers the astral holds and, ultimately due to exposure to those energies, damage his physical body including his physical eye-sight.
The Nodes are 180 degrees apart, like ying /yang, consuming one house and expanding the other exactly opposite.
Rahu in 1st Ketu in 7th Now your over-reaching self-ego consumes partnerships. Desire to win at any cost dissolves legal bindings. Being first and prominent in the society stops fairness and equitability. You are aggressively self-promotional and really not bothered about your equals and partners. Take care of your marriage, these 18months are one thing but husband/wife is forever!
Rahu in 2nd Ketu in 8th You develop ambitions about increasing your wealth and assets and maintaining them for your use. Desire to be in control of the family treasures and using them for your own purposes. You want solidity, material things you can touch and increase. And on the other side, you have no desire to change, to transform and to re-invent yourself. The secrets of the mind, of the esoteric, the tantra, the intangible but powerful magics hold no charm for you. Do not let your family members over-ride you.
Rahu in 3rd Ketu in 9th You desire local trades, siblings and neighbourhood. Lots of quick communication, gossip and chit-chat. Juvenile behaviour and adolescence. Also superficial analysis which will lead to profits. No inclination to associate with the betters, peers, philosophers and patrons. Disinclined to reflect, ponder and philosophise. You know how to work the stock market for even more money but will not think about the theory of role of money in the society. Do not let your siblings get the better of you and do not get cut off from the philosophies that are the foundation of your life.
Rahu in 4th Ketu in 10th Here you superficially desire maternal security and comfort zones. The stability of the physical structures and even customs and traditions. However you will neglect your father and your profession, your power and position in the society. Intent on your personal emotions you will not be aware of the demands and obligations of the society and the work that you are expected to perform here. Remain in your senses and do not let mother/maternal figures get the better of you. Take care of your father, you may lose him.
Rahu in 5th Ketu in 11th You will be highly self-referential during this period. The world will revolve around you and your sense of intelligence, genius and creativity. You will superficially talk about high ethics and morals. You will be in the center-stage, drama, politics or any expression of individual self-expression. However you will neglect the greater networks of humans and like-minded groups. Your source of income will be in spurts not a sustained flow of money. Do not let your children force you into unpleasant situations.
Rahu in 6th Ketu in 12th You will actively seek the forces who can potentially harm you in the context of disease, debt and enemies, and you will vanquish them. This will help you in balancing your karmic debts and the records that are maintained in the astral realm will not affect you adversely. However you will not receive guidance from your astral guides either, your sub-conscious will not be so accessible and dreams/visions will not be so helpful either.
Rahu in 7th Ketu in 1st Now you will put your partnerships before any selfish gain. You will respect the legal demands that others have on you at least on a superficial level. You will try to uphold equitability as long as your interests are not affected. Do not let your partners get the better of you. You will be not bothered about your social standing and ego, if you do some spiritual practice during this period it will be fruitful. Take care of your personal health.
Rahu in 8th Ketu in 2nd You will be dissociated from your family during this period. Loss of wealth resources is indicated. The secrets of the mind, of the esoteric, the tantra, the intangible but powerful magics will attract you. You will want to forge new identities for yourself. You might spend money and wealth unnecessarily in these. You might suffer secret diseases, reproductive organs problems, accidents, surgeries and diseases related to over-heating.
Rahu in 10th Ketu in 4th Here you will give in to the demands and obligations of the society and the work that you are expected to perform here. You will superficially behave as the ideal worker but as always you will have your hidden agenda. You might ignore your emotional and comfort zones and work. You will be more in touch with your father but do not let him over-ride your decisions. Take care of your mother, you may lose her.
Rahu in 11th Ketu in 5th You will mingle with the greater networks of humans and like-minded groups. Your source of income will be a sustained flow of money from several sources, don’t get into illegal activities. You will prefer anonymity rather than the center stage and you will work systematically. You will prefer to work for the greater good but only till your personal interest is satisfied. Do not ignore your children and maintain a hobby during this period.
Rahu in 12th Ketu in 6th The forces who can potentially harm you in the context of disease, debt and enemies, will auto-destruct. You may suffer very briefly from disembodied entities/ghosts. The records maintained in the astral realm will be available to you and your astral guides, dreams/visions will also help you. Rahu being a superficial pretender will prevent you from getting too immersed in the astral too.
These are of course the overlying trends which will last for 18 months of their transit in each sign/house. Pay attention to which Dasha you are on. Transits are always coupled with dashas to get a full picture. These trends will be further modified by the trends in the other planets transits and the original chart/placement. If you have special combinations involving Rahu Ketu like complete or partial kaal sarpa in your birth chart do that in-depth analysis first. Having a well-balanced birth chart is a huge asset as then the transits cannot cause much mischief.