Learning astrology is like a tracing through a wheel. There is no one starting point. Just start reading, understanding and thinking over astrological concepts. Take any basic book from any of reputable astrologer and read it, understand it and think over it.
And try to observe astrology in every day life. Picture Astrology.
An Astrologer must be most keen observer of life. Astrology is nothing but framework of life; just like Trigonometry is framework of Triangles. Once you learn Trigonometry you can understand everything about any kind of Triangle. Similarly once to learn and understand Astrology you can understand about phenomenons of Solar system and life.
Here is a simple exercise - For few mins observe and think about each day's happenings in the night. See which day of the week you are most joyful and which days are going stressful. And see how it relates to your current transit and dashas.