Predictive Astrology involves using tools to help predict upcoming events and plan the best times to make changes in your life. There are two major tools used in predictive astrology: Transits and Progressions.
Transits are where the planets are right now, as opposed to where they were when you were born. Mapping the planets at the time of a chart reading against the positions they were in at birth, an astrologer can explain what areas of your life are being emphasized, what major events may transpire in the future, and what options you have for dealing with the energies that are affecting you at that point in time.
For example, Saturn (restrictions, delays, practicality) may be moving through your 10th house of career. Saturn takes about two-and-a-half years to move through a sign, so it will be in your 10th house for approximately that length of time. This transit could bring some major changes to your career life, the nature of which will depend upon a number of different factors. You may take on more responsibility at work, receive a promotion, find yourself working hard for little reward, or even retire. It depends on the aspects the transiting Saturn is making to the rest of your chart and to any planets in your 10th house, and the signs and natal house positions as well.
Let's say Saturn is moving through Taurus in your 10th house. Next month, transiting Saturn will form a trine to your natal Mars, which is in your 2nd house of earned income. That sounds a lot like a promotion with a pay increase.
If, however, transiting Saturn formed a square to your natal Mars in the 2nd house instead, this might more accurately represent the lack of a raise and promotion, and even difficulty with your employer.
Transits represent a temporary state of affairs, and should be interpreted keeping the meanings of your natal chart in mind. If your natal Mars was in a very good position in your chart, the transiting square from Saturn might only mean missing a slight raise or having a delayed raise. If, however, your natal Mars is very difficultly aspected, your boss might fire you because you were too aggressive in your pursuit of that raise!
You can also pay attention to transits to the midpoints (An unoccupied aspected degree between and equidistant from two other planets, resulting in a symmetrical grouping, sometimes called a planetary picture). of your chart. I personally find transits to midpoints to be very strong, and easy to accurately time. Of course, the transiting planet in this case would need to be assessed against both planets involved in the natal midpoint, as well as all the other usual factors.
Timing is a difficult thing in astrology in terms of prediction. There are numerous methods out there, and great disagreement on what method to use, and what orbs should be given to transits. I agree with Rob Hand and others that multiple transits (when more than one planet is transiting the same area of the chart) are timed best by the faster moving planet. So if Pluto is aspecting your Sun (which could be over a period of several years), and Mars comes along and hits the same place (which it will in that time frame), look at the date when Mars will make the aspect for the date when you will most feel the influence of Pluto's transit.
My opinion on orbs is that two degrees for most planets does the trick in timing transits. For instance, when Mars approaches your Sun but is two degrees from exact, start expecting an event to occur, and don't stop expecting it until Mars is two degrees past your Sun. Oddly, I have found from personal experience that transits often hit harder at two degrees before or after than they do when they are exact.
The Moon moves so quickly that transits from it rarely have any major impact. If you are ruled by the Moon, however (either a Cancer by Sun-Sign or a Cancer rising chart), you may feel its impact more strongly than others. Generally, the Lunar transits relate mostly to small day-to-day activities and moods.
Outer planet (Uranus, Neptune, Pluto) transits affect some people strongly, some less so. If your outer planets natally are strongly placed by sign and house, and are closely aspecting your personal planets, you will obviously feel the outer planet transits more strongly.
Progressions can sometimes act like transits in setting the stage for external events, but are more usually indicators of your inner growth. Progressions are a symbolic system of accounting for inner growth. Our natal charts are a map of potentials given to us when we are born, but almost none of us stays stuck in our potentials at birth. We grow; we experience; we learn; we change. Our progressions reflect this.
The most common type of progressions are secondary progressions. To find secondary progressions, we use the Biblical guide of "a year for a day"; in other words, each day in the ephemeris represents one year of an individual's life. Thus, if you were born on January 1st of the year, you would look at January 2nd to represent your life at a year old, and so on.
Since the outer planets move so slowly, they will move very little within any individual's lifetime. They may come to an exact aspect which is inexact in the natal chart, and this will bring the potential within that aspect to fruition within your life. And the outer planets may also turn direct or retrograde, which will change the way that planetary energy is expressing in your life.
It is the inner planets (Sun, Moon, Mercury, Venus and Mars) that are most significant in progressions. You can interpret them similarly to transits, keeping in mind that they represent your inner growth more than outer events. For instance, transiting Sun conjunct your natal Mars is an annual event which can represent activation of Mars in your chart (energy, sexuality). Progressed Sun conjunct your natal Mars could more likely represent a time in your life when you are coming into your own in terms of knowing how to use and express your energy more effectively.
The progressed Moon takes approximately one lunar month (about 27-1/2 days) to make one entire trip around your natal chart. This is a significant time in one's life, at age 27-28, and coincides with the return of transiting Saturn to its natal place (at about age 28-29). It is usually a time for major life changes and decisions.
The other major form of progressions in astrology are called primary directions. This simply takes the motion of the Sun (approximately one degree), and applies that motion symbolically to all the other planets as well. This allows the outer planets more significance in progressions, as they will move through two to three signs within each individual's lifetime rather than the few degrees they normally are allowed in secondary progressions.
More on najaramah.com