Over time, a wizard uses a particular evocation often enough that it settles into mental “muscle memory,” and its use becomes reflexive. When this happens, the spell is considered to be a rote spell. Your wizard may know a number of evocation rotes equal to the numeric rating of his Lore skill. So, a wizard with Great (+4) Lore knows up to four evocation rotes.
A rote spell is defined as one specific application of evocation in a single element, such as a fire attack, a particular air maneuver, or a spirit block. It always manifests in exactly the same way each time, has the same power level, places the exact same aspect, etc. Any change in the parameters of the spell disqualifies it from being a rote.
The big benefit of knowing a rote spell is that you don’t have to roll Discipline to control it. It’s assumed that you can control the spell energy at a level equal to your Discipline score, allowing you to act as if you’d rolled a zero on the dice every time. You still need to make a Discipline roll to target the spell, however; there’s just no chance of accidental failure.
Focus items add their bonuses automatically if they are tied in to the rote, but there’s a caveat: if the wizard does the rote with the focus item, then that item is a requirement for the rote every time he wants to use it. (This is why Harry gets so nervous about entering combat without his staff and blasting rod—he loses the benefits of the rote spell and has to roll each spell as a normal evocation.) Aspect invocations and other such trickery may be used after the fact, just as if you had rolled a zero and then wanted to invoke something.
Harry has his “Fuego!” spell as a rote. He can choose not to make a control roll when he attacks a single target with fire magic. His blasting rod is tied into the rote, giving him an effective Great (+4) Discipline controlling the spell. With his Conviction, he has no problem producing four shifts of power for the spell, so that’s where he sets the power dial. Therefore, the rote spell is a Weapon:4 fire spell automatically.
Finally, keep in mind that you can have a rote that’s more powerful than you can control with a Discipline roll of zero, which would basically cause automatic fallout or backlash when used unless you can invoke some aspects to make up the difference. This is clearly not for the fainthearted, but it might be useful as a sort of “last resort plan,” making sure you can put the heavy damage out there in a moment of dire need.