I was fortunate a couple years ago to live in an area of the Catskills where the yarrow grew wild and free, and finally had the opportunity to read the I Ching oracle in the traditional manner. I had used three coins to count the lines for years so it took me a few tries to figure out how to use the yarrow stalks.
This method puts you into a meditative and receptive state of mind. Yarrow encourages this because it is a plant that collects energies and sends them spiraling down through it’s hollow stems. The counting becomes a mystical experience with the sound of the stalks clicking and resonating together as they are thrown down, or collected together. Then, when the hexagram is formed, taking time to understand what the I Ching is saying and how it relates to our situations. The whole practice is a wonderful exercise that gets the whole body, soul and mind( on both individual and collective levels) involved.
Most of the following instructions can be found at the back of the translation of the I Ching (or Book of Changes) by Richard Wilhelm. I highly recommend this book for understanding the hexagrams.
It is a little difficult to show all of the possible alternatives in one instructable but I hope that this will help to demonstrate how a reading is done using wild yarrow stalks.