The process has never been formally documented so far. If you carefully search this category (FFH) you will find several threads where we have been explaining how we get new Staff in, and that's it
For several years, integrating new Staff people has been a rather easy process : current Staff would suggest new names, the FC (in particular ubuntu-geek and matthew) would work on a list and selected people would get invited to join.
With the strong and steady expansion of our community, the process needs a better definition so that other FC members can handle it too. We will continue to ask the current Staff for suggestions, it has worked really well so far.
We have been adding new Staff roughly before every new Ubuntu release, before a jump in user number, so that people have time to adjust and learn the tools and habits. Two volunteering FC members will be delegated to handle the process.
Four main steps take place :
a) A post is created in the Staff area asking for suggestions
b) Two FC members compile a list of names from the suggestions
c) They present the list to the FC to vote on
d) They approach the new Staff by PM and ask them if they would like to join
After they accept, new Staff forums permissions are adjusted to place them in the UF Staff group and grant them access to the appropriate IRC channels.
Once a year, the delegated FC members will track Staff who are MIA.
bodhi.zazen and myself have volunteered and been designed by the FC to take the lead on this project. Matthew will mentor us as he had been taking care of the process with UG so far.
The essential part of this post has been documented in the Forums FAQ and linked in the Guide to Forum features.