I have the 1989 edition of this book, and find that it's one of the best intermediate level books for learning astrology. It is also organized as a detailed, intelligent, and subtle reference source for professionals. This book details basic meanings of signs and planets, as well as planets in signs and houses, angles, and rulerships. You will need your own charts or chart data.
Popular astrology, as most people think of it, deals exclusively with sun signs -- the astrological sign in which the sun was located at your date of birth. But the moon and each of the planets were also in a sign when you were born -- and each might be in a different sign. Serious astrology takes into consideration your moon sign and the signs in which each planet was located at your birth time, as well as your sun sign. This collection of the positions of the "lights" (sun and moon) and planets in the zodiac of signs makes up your personal horoscope. Also important are the angles (called "aspects") which the lights and planets make with respect to each other. All of these factors -- plus the astrological "houses" -- are explained both simply and clearly in this excellent introduction to serious astrology. If you want to go beyond "newspaper astrology" this is the best book to start with.