Q: How is it when you open up a horoscope of a question, of a seemingly arbitrary moment in time, that it can answer questions about the wider range of reality all around the world?
A: It is because it is a sample of a larger, interconnected reality. (Example: physician uses a sample of your blood to determine what all is going on inside you because your blood sample is a representation of the greater whole.
Astral Light interconnects the entirety of the universe. It is a fluid which binds the spiritual, the physical and immaterial all the way down to the most basic substrates of reality. (When you take a sample of it, it can tell you anything about anything past, present or future.) - this is how Divination works.
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The above is not only one of the best explanations of divination and how it works it is also an excerpt from a video by Clifford H. Low on traditional astrology. The idea is that divination is nothing more than a sampling of a larger, interconnected reality. Once you start studying the ancients like Iamblichus, Trimethius, Agrippa, Lilly and so on, you begin to understand that these old dead guys knew a helluva lot more about the universe than our modern subjective psychological models offer.
As a practitioner, you should learn SOME FORM of divination and learn it well. Really well. Well enough that you are comfortable with it anytime you need to peer into someone's personal reality including your own. I recently ordered Willliam Lilly's first two books on astrology and these have to do with learning how to set up, read and interpret horary charts. Horary astrology deals with divination for questions which was the leading type of use for astrology in ancient times.
A question was asked, then the time and location was noted, factored into the reading and a natal chart was cast for that exact moment. The judge aka the astrologer also known as the interpreter, would look at the first house, where the Moon was in the chart (sometimes it did not matter at all in certain readings) and then the house for the question was seen and its significator. From there other factors were looked at but those were the basics.
Divination with Tarot cards is the same because it's a reading or sampling of a much larger whole. So to with any form of divination or prognostication. This is how the ancient Greeks saw the larger universe by peering into the micro-universe in front of them. 
Cards didn't become in vogue until the medieval period in France but the ancients used sortilege or the casting of lots to determine many things as well as for direct communication with spirits who refused to verbally commuicate. We know pendulums were found in toms in ancient Egypt and they were necessarily for plumb bobs either. Divination by dice was an ancient method referred to as the Holy Astragals which uses two 6 sided die and a 12" circle. You shake the dice in your hand and ask the question then roll the dice to the circle. Only read the dice which fall INside the circle. Thus you can get answers for 1-12.
Astragals: A Simple Method of Sortilege
by Brother MOLOCH 969
©2014 All Rights Reserved
http://www.molochsorcery.com
Sortilege is often viewed differently from traditional forms of Divination like Tarot, I Ching and Oracle Cards because it relies on communication between you and a spirit - be that spirit a patron, a deity or someone you summoned or conjured. Instead of trying to use complex layouts with cards that have intricate and detailed symbology, sortilege is often just casting lots in a manner to divine quick, short term answers to specific questions.
The questioning is all important as you need to learn to ask specific questions that can be answered in a yes or no format. This is a very simple and elegant method of getting complex answers by asking a series of yes/no questions that cover whatever it is you’re asking about.
The problem with it lies in the fact that this sort of questioning is both tedious and depending on the complexity of the situation, it can also become time consuming. The results however are quite stunning especially when you find a spirit who is willing to communicate through the dice.
A method of sortilege you may want to try is the Holy Astragals or commonly referred to as just the Astragals. This is where you employ two six sided dice and a mat (I use a piece of leather but poster board works quite well) onto which you've drawn a 12" diameter circle.
You then speak your question aloud using a Yes/No format, meaning you ask the question so that the answer can be given in either a Yes or a No, then shake the dice in your hand and roll them towards the circle. You only read the dice that lands inside or on the rim of the circle.
If one of the die lands outside of the circle, then it is ignored; if both dice land outside of the circle, then you scoop up the dice, ask your question again and re-roll towards the circle. If both dice land inside the circle, then the number for each die is added together and the result is looked up. Here are the 12 possible answers:
1 Yes
2 No
3 Be Careful (a warning in relation to what you've asked)
4 Be wise (think this thru)
5 Good Luck (a positive answer)
6 Of course (a positive answer)
7 Be strong in faith
8 Be patient (it will come to pass in time)
9 Quite sure (this is an emphatic YES)
10 Doubtful (a negative answer)
11 Nonsense (inconclusive answer - reformulate question & ask again)
12 Stroke of Luck! (considered a very good omen)
Note: If you get a Be Wise or Be Strong in Faith type of answer the best thing to do is to re-ask your question but word it differently as I’ve found this helps out a lot for clarification purposes.
With this system, you can work with (just about) any spirit and communicate with them. Then you can ask specific questions (always in a Yes/No format of course) so that you can determine formulas for potions or ingredients to include in a spell &/or ritual. Yes this IS a tedious method however it is far better than guessing or not using one at all.
Thus you can ask questions like:
Should I use a blue candle for peace in this Uncrossing ritual? While you may think "Of course!" the spirit may deem it is unnecessary. Or perhaps you're wanting to do the all important Money Drawing spell? Okay so you bought a green pillar candle and now you're not certain which money oil you should dress the candle with. Thus you ask a series of questions...
Should I use Money Drawing oil on this candle? A: 2
Should I use Wealthy Way oil on this candle? A: 10
Should I use Prosperity oil on this candle? A: 7 (reformulate question, ask again)
Should I dress this green pillar candle with Prosperity oil? A: 3 (a definite No)
Should I dress this green pillar candle with Horn of Plenty oil? A: 5 (Good Luck - a Yes answer)
Thus you now know to dress this candle with Horn of Plenty oil. Now I have had to go through my entire list of money oils sometimes twice before the spirit chose one. Rare that is but it happens. But when you're a practitioner without a familiar spirit guiding you directly, this is how you do such things and get reliable results. Rank amateurs simply guess at what they should use and often they're wrong so they get upset when what they've invested in doesn't work.
Let's say you're making a gris-gris bag for protection for your nephew who has been bullied at school. Again you contact the spirit or simply lay Its seal in the center of the circle and then begin asking the questions such as:
"Spirit __ I'm making a protection bag for my nephew who is being bullied at school and I need to know what specific items to include in this bag of protection."
Then begin with a list of protective herbs/roots you have on hand and one at a time ask if you should include it or not. If maybe comes up, the choice is left up to you. Just go down the list of ingredients and ask one at a time until you have exhausted the list. Then you can ask about protective stones and crystals to include (or not); charms like crosses, rosaries, and other tokens you can buy at botanicas; dirt from crossroads, banks, jails, hospitals and etc if they're needed or not - only those you have on hand you need ask about; oils to dress the bag with; and so on.
The THREE DICE Astragal patterns are cast the same way as the 2 six sided dice Astragals except that this set does not work with a circle. Just roll them together and add up the face value and read from this chart:
03 unexpected but favorable developments
04 Dissapointments or Discontent
05 something you want will come to you in an unexpected way
06 Discouragement especially in business matters
07 Delays possible through Gossip
08 Strong outside infuences
09 Omen of love & harmony or Reconcilliation
10 Birth Promotions or New Beginnings
11 parting with loved one
12 letter of good news
13 unhappy development
14 a friend helps you or new aquiantance becomes a friend
15 careful avoid temptation
16 good sign for travel
17 change of plans
18 Happiness & Success
The two 6 sided die method was introduced to me by famed occultist, Brujo Negro back in the late 1990's and I have used this method extensively. A British occultist turned me onto the three 6 sided dice method for expanded readings and while useful, I still prefer the two dice method better.
Learn a form of divination. Study it well. Practice doing readings for people even without their permission. (You don't need to tell them you're doing this! Especially since you do not plan on telling them anything - just write down in a notebook what the results were so you can keep track of your accuracy as you watch their life unfold.) Practice, practice, practice. The more you practice the better at it you will become. Divination is a tool every legitimate practitioner should know how to do. No one who is a spiritual worker goes to someone else for divinations when they can do their own.
If you don't "trust" your judgment, then you've screwed up somewhere. This is not rocket science folks. It is a method of communicating with spirits about the complexity of a person's life as viewed on a microcosmic scale via a system of divination. Choose a method. Learn it. Be patient. Practice. Know your craft.