The Beginning of Wisdom by Abraham Ibn Ezra, trans. Meira Epstein (ARHAT Publications, 1998)

Judgment:  A good reference source for universal astrology, including information and aphorisms that are hard to find or otherwise not available.

Abraham Ibn Ezra (1089-1164 CE) was a medieval Jewish scholar who wrote (among many other things) a number of well-regarded astrological treatises. The Beginning of Wisdom is the second of a projected series of translations of Ibn Ezra by Meira Epstein. 

Apart from the biblical reference in its title, this book forms a "beginning" because it is primarily devoted to universal astrology, i.e., basic principles of astrology relevant to all branches: signs, fixed stars, houses, planets, weaknesses and strengths of planets, the relationships of planets to each other, Arabic Parts, and a short section on mundane astrology.  It does not contain any systematic treatment of horary, natal, or mundane astrology.  It is therefore similar to Alchabitius's Introduction and Abu Ma'shar's Abbreviation of the Introduction, both of which were written in the same Arabic tradition.  But Ibn Ezra goes beyond those other works by incorporating material that is useful for magical-spiritual practices as well as techniques in specialized fields.  For instance, of interest is his exposition of the decans, their magical images and application in medical astrology and physiognomy (as it was handed down from antiquity). 

But even more compelling is the lengthy chapter devoted to aphorisms for judgment.  Although students of astrology (and especially medieval astrology) know that Mars and Saturn are malefic, or that retrogradation is not a good thing, it can be difficult to weigh these factors when trying to make a judgment on an actual chart.  Medieval astrologers developed a number of vivid analogies, metaphors, and aids to help one do just that.  Even more than Morinus, Ibn Ezra provides handy and thorough lists of what planets in the houses and in relation to each other really mean.  For example, "A planet in the 6th house is like a weak man running."  Or, "When Jupiter aspects the malefic, it changes its nature into benefit, yet Venus cannot change the nature of Saturn, except with the help of Jupiter.  Therefore, Jupiter removes the harm of Saturn, and Venus removes the harm of Mars [even] more than Jupiter [does]."  These sorts of comparisons and analogies are of great help when trying to figure out what a planet is actually capable of in a nativity or horary question.

I would recommend The Beginning of Wisdom as a good reference source that is handy and thorough, and often prevents one having to consult several sources to get clear guidance.