All of the planets move around our Sun in the same direction and have their own cycle time depending on their distance from the Sun.
Retrograde motion is in fact an illusion as it appears as though the planets slow down and then move backwards.
What actually takes place is that the planet in question makes its closest approach to the earth and gives the viewer the false visual that it is moving backwards.
The planets all go into retrograde and then direct throughout their full cycles around the Sun. The outer planets are in retrograde about 40 percent of the time (and their energetic affects are generational).
The inner planets go in retrograde for shorter periods of time. The inner planets (Mercury, Venus and Mars) are said to be personal planets and when in retrograde are the most challenging and often require inner reflection, alignment and adjustment. They will force us into action, and this action required is often the best approach once the planet in question has turn direct once again.
It should be noted that if you have a retrograde planet in the birth chart and when it receives an aspect from the same planet transiting in retrograde, the energies will be more intense than for someone who does not have that particular planet in retrograde in their natal chart. It should also be said that it needs to make a direct aspect within five degrees to have a meaningful impact in our lives. The more planets it touches by aspect the stronger the influence.
Jupiter and Saturn are in retrograde approximately one third of the time and are considered less personal and less of a challenge. It should also be noted that when a planet is in retrograde, the normal flow of energy is disrupted and often held back or stifled. Saturn is the exception. Saturn’s energies are actually less restrictive and delayed in retrograde motion. It is considered more favourable in retrograde than when it is in direct motion.
When planets are in retrograde it is a time when we need to reflect and to put our focus on decision making. It is a time for making plans and to change our objectives or our perspective on what this retrograde cycle would be implying. It is important to take into consideration the planet in question and its position in our chart as well as any aspects it will be making. If it crosses a planet for example by conjunction when it turns direct once again it will move across that same position and the energies in place will once again be intensified.
There is also a period called stationary retrograde and stationary direct when, for a few days up to several days, the planet appears to be stationary or not moving at all. It slows down and then stays at the same degree for a short period (the length of time will depend on the planet as some planets will stay in their stationary position longer than others). When it is in this stationary position, the energies are at their strongest and will be intensely felt especially if the transiting planet in question touches a natal planet at the same time.
While in retrograde, you should resist taking action. Know that once the planet goes direct, it is time to take physical action. Pay attention to what these energies are pointing towards (planet, sign and house position) and make plans so that you can set them in motion when this retrograde period is over (except as mentioned with Saturn as its energies are less obtrusive in retrograde motion).