Darkness in New Orleans
A rote is a tried and true effect that has been practiced enough that the Mage no longer takes the "fast-casting" penalty of +1 difficulty for the effect. Mages do not begin play knowing any rotes (although on rare occasions I might allow it with the expenditure of freebie points).
To add a rote to your character's repertoire, first, give it a cool name. Second, figure out what you want the rote to do. Third, figure out what spheres are required (if there is any doubt please consult your Storyteller). Finally, practice the rote. Track the number of times you have used the rote successfully. Once you have used the rote successfully ten times, you may record it as a known rote and you no longer incur the +1 difficulty for fast-casting penalty when using the rote.
Note: you may only work on one rote at a time. But there is no limit to the number rotes your character might know. At any time you may decide to stop working on a rote and begin learning a new one, but all successes earned from the previous rote are erased. If you ever go back to learning the previous rote before you must start from scratch.
Example: Sike is a Virtual Adept who wants to learn Landscape of the Mind, a Correspondence 1 rote (from Mage Revised). Sike begins practicing Landscape of the Mind and has built up six successes when she decides she would rather learn Perfect Time, a Time 1 rote (also from Mage Revised). She erases her successes on Landscape of the Mind and now must earn 10 successes on Perfect Time before she has learned it. Once she does so, she can go back to learning Landscape of the Mind (although she must start again from 0 successes and get 10 more to learn it) or she can learn another rote.