In addition to visualizing Manjushri, it is recommended that the querent recite his mantra: OM AH RA PA TSA NA DHI (either 3 or 7 times). There are further rituals (and a lot of other information) that you may learn about in the book Mo: Tibetan Divination System by Jamgon Mipham (translated by Jay Goldberg).
The 6 last syllables of the mantra above are on the 6 sides of the traditional Mo die, but we can use regular dice by adapting the dice like this:
Numerologically the syllables correlate to the elements, body parts, directions, senses, and activities.
Relationship casts are also done with two rolls of a die, but in this case the first die represents yourself and the second is the other person. As in other methods of divination, the relationships between the syllables should be your main focus.