How to sponsor a new contributor
Sponsoring Someone for Fedora Package Collection
Sponsoring someone for access to Fedora Package Collection is relatively simple. If you are looking for someone to sponsor, take a look at the Fedora Account system for contributors who are currently searching for a sponsor. Note that they should also have submitted a package review request for a package which they are proposing to add to Fedora on  . In this request they should write, that they need a sponsor.
Bugzilla will send a notification mail for the new review request to the fedora-package-review mailing list. Take a look at their package and review it. If it looks reasonable and it seems that the comply with the Packaging Guidelines , then they are probably a good candidate to be sponsored.
Add any comment for changes to the review request on Bugzilla which look as though they'd be needed for compliance as well as the fact that you're volunteering to sponsor them. Once they've made those changes, you can approve the package and click the appropriate link to sponsor them for access.
Once they have CVS access, you should be sure to review their commits to the CVS repository for how they look, and consider watching their Bugzilla activity at least for a while (Account->Email->Users to watch). Respond with any comments that you might have and guide them, providing assistance as they need it for any tasks.
So what's the downside to sponsoring someone? By sponsoring someone, you are committing to the fact that if they break something you will fix it (or help them in fixing it). Additionally, your sponsoree will likely have questions about processes; one of your responsibilities as a sponsor is to help them with the answers. A sponsor isn't expected to be omniscient, though, so you can feel free to ask for others' advice and opinions if you get a really hard question.
Becoming an Fedora Package Collection Sponsor
Fedora Package Collection has been setup so to encourage "learning by doing" and the development of cooperative relationships between Fedora packagers. To date, advancement to a sponsorship position has been an undocumented yet somewhat formal process. Within the project, people have (and continue to!) develop reputations by creating packages, performing reviews, helping others with their questions, and generally doing what they can to advance/improve Fedora packaging.
When someone within the project has developed a "good reputation" (and this is admittedly a somewhat fuzzy definition!) then someone else will generally nominate them for sponsor status. Nominations can be sent to the fedora-devel-list , directly to the Fedora Engineering Steering Committee Chair, or in-person during the appropriate portion of a Steering Committee IRC meeting. A discussion and vote will then occur during the next Fedora Engineering Steering Committee meeting.
How To Get Sponsored
If you are looking for more information on getting sponsored yourself, take a look at http://fedoraproject.org/wiki/PackageMaintainers/HowToGetSponsored