I participated from the first cooperated suite ever, Polymer, by The Skindicate with 2 friends, Dangeruss (my allways master) and Demer. For that suite I made the windowblinds skin and the NextStart theme first, then all the other skins came porting those 2. We have skinned 35 applications.
I also participated from the second and bigger suite. The first Community Skins project, on wich, over 40 skinners made their contrubution to make around 65 skins for different programs.
That project was leaded by Chad aka CRUMBUT (someone that i terribly miss in the community). He made the windowblinds skin and we followed him.
Other Community skin projects came after that, but unfortunatly I couldn't particapete anymore.
I would like to do more community skins, but unfortunatly today, my major job (professioanl skinning 
) doesn't left me too much spair time for this.
This is really said to me, because of the GUI Olympics, I find myself very pleased skinning just for fun....it was a great pleasure doing thoose skins.
What i can give you guys is a few tips, because as was already said above, there are no rules for that.
1) Let just one, max 2 persons, to make one killer windowblinds skin. As soon as it is done and aprroved for the first members, the authors releases to the other memeber, a set of all ellements of the skin in a PSD or other layered file, so the other can know how the effects were done.
2) Decide a list of the possible apps to be skinned
3) Decide between you who will make what skin
4) Variations of the first skins can ocour, but try to stay fix in some points, like fonts, color text, etc... also like buttons can be changed, but never missing the spirit of the mother skin.
5) Try to do everything talking eachother by email, with copy to all involved, so everybody know what is happenning at the same time. The same for screenshots etc... In the first Community project we even had a private forum and ftp, because we were too many.
I really hope this project go forward and good luck to you all. 
