wizzle said:
1. Back when I was studying astrology decans were confined strictly to their elements. The first decan of Aires is aires/aires, the second aires/leo, the third aires/sag. So on for the rest of the elements. Just start with the sign and then go on to the next sign with that element for the second decan and to the third for the third decan. Piece O cake. I admit this was a zillion years ago and based on Allen Leo's books but I doubt the stars have changed all that much.
This method, which though known about in medieval Western Astrology, is that used in Indian Astrology, it was popularised in the west in the late 19th and 20th century by the english theosophically influenced school of astrologers [leo, carter, et al].
In traditional western astrology the faces are ruled by planets, running in Chaldean order starting with Mars as ruler of the first face of Aries. If you know the Chaldean order then you can easily work out which planet rules which face if you remember Mars the ruler of Aries rules also the first face of Aries, ergo the second face must be the Sun [next planet in the chaldean order], third Venus, fourth [first face of Taurus] Mercury etc.
Another way of working it out is through the relation with the days of the week, that is Mars, which is Tuesday rules the first face of Aries, the next day Wednesday, ruled by Mercury, is the first face of Taurus, Thursday - Jupiter - first face of Gemini, Friday - Venus - first face of Cancer, etc until you get to Saturn - Saturday - first face of Pisces, then you jump to Sunday - Sun - Second face of Aries, Monday - Moon - second face of Taurus, round to Thursday - Jupiter second face of Pisces and then you jump with Friday - Venus - to third face of Aries, around the third faces of the zodiac again ending with Tuesday - Mars - third face of Pisces.
Of course astrologically speaking the fact that the first face of mars is ruled by Mars is not technically the same as Mars in Aries; although some, and I think Crowley among them, do often interpret the meaning of the face that way.
Kwaw