FIMing is a hit or miss kinda thing. Sometimes the magic works...sometimes it doesnt.
I had some plants on my deck rail last summer that got knocked off...and fell two stories. They were mangled to hell. So, I cut them back to about four inches, not even trying to FIM....just cutting off the broken part. To my amazement, they all came back. But one....accidently FIM'd, grew four equal heigh colas and looked kinda like a calendebra...four equally tall colas in a horizontal line. Beautiful.
When it works, it's great. However, depencing on exactly how much of the growing tip you remove, you may or may NOT get the desired effect. Still, all we can do is try and hope for the best.
I dont think there is really a "preperation". You just gotta trust god or nature, LOL...and cut that growing tiup. Leave 20% of the growing tip. With LUCK, you will get three or four or maybe five new colas. At worst, you will get two.
Good on ya!
CW