The study of transits is especially valuable because it allows us to get a sense for the timing of the planetary archetypes in our lives. Perhaps of all areas of astrology, it is the study of transits that produces the most compelling evidence for the power of the astrological perspective, and its immense pragmatic value. The principle of transits rests on the fact that as the planets continue moving after a person’s birth, they move into and out of aspect in relation to the natal planetary positions. Thus when any planet's present position in the sky forms an aspect to a point that was occupied by any planet at the time of one’s birth (for example Uranus now in the sky forming a conjunction to Venus in the natal chart), then during the period in which that particular aspect is in range one would tend to have experiences that correlate with the planets and aspect involved (in this example, a two-or-three year period in which one would tend to experience the awakening of new love, the stimulation of one's artistic creativity or aesthetic responsiveness to life, a certain restlessness and unpredictability in one's relationships, and so forth).
While the birth chart in itself is a portrait of one’s life and character as a whole, transits to the birth chart reflect the dynamic unfolding of one’s life and character in terms of specific events and experiences. Transits activate the potential that is inherent in the birth chart.
Since different planets move at different speeds, the duration of their transits varies--a Moon transit lasting only several hours, a Sun or Mars transit several days, and the outer planets several months or even years. The transits of the inner planets are useful for understanding the day-to-day changes and shorter cycles of one’s life, but it is transits from the four outermost planets--Saturn, Uranus, Neptune, and Pluto--that are of the greatest significance in understanding life's larger dynamics.
There are a number of other significant factors in the birth chart that are well worth examining, such as the sign positions of the planets (Aries, Taurus, Gemini, etc.), the houses, the elements and qualities, hemispheric emphasis, harmonics, as well as other predictive techniques such as progressions, solar arc directions, solar and lunar returns, etc. I find all of these to be valuable factors to explore, and I may at times bring some of them into discussion, but my own particular expertise, as well as the bulk of my empirical research, is in the area of interpreting the combinations of planetary archetypes, the major aspects (including midpoints), and transits. I regard these, after many years of research, as the most essential factors in astrology, possessing great precision and richness of meaning. These factors reflect a certain beautifully lucid geometry of archetypal forms and forces, and I believe they offer the most intellectually cogent and clarifying path of entry into the mysteries of the astrological perspective.
I recommend seeking out interpretations or readings from every good astrologer who crosses your path, for astrology is so complex, and your chart has so many facets and levels of meaning, that each astrologer can illuminate it in new ways and give you important new insights. Also, my own focus is on the psychological and spiritual dimensions of life (as well as on long-term cultural and historical cycles). There are other astrologers who focus on medical, financial, horary, and other specialized areas of astrology, which you may find particularly relevant to your own interests. But beyond getting readings from good astrologers, I believe the most rewarding path to take in the end is to learn something about the field for yourself, learn how to calculate your own transits (it is not difficult), and then examine the evidence and experience this profound source of insight and understanding for yourself.