To prepare I watch a few videos to get the feel for the encounter space we have to work with and keep an eye on any space limiting abilities (ie: ooze puddles). I then read over the abilities and then try to play out in my head how they will effect the raid.
Afterwords I post the videos and abilities available on our guild websites boss strategy section for the other raiders to review. I don't feel that spoils it so much as it allows us to be prepared in some form. Reducing the amount of wipes generally increases the fun for all.
I did PTR testing once for Ulduar. There was a giant patchwerk that would eat your face if you looked at him wrong and an empty instance. Though I agree some good information can be found on the PTR, I think that spoils it a bit more.
I think having a basic understanding of the abilities and the encounter space goes a long way. The rest is learned in actual attempts and tailored to how your guild raids.
There is something so appealing about backhanding someone across the face with a shield.