Install the necessary tools
yum install git livecd-tools
Have access to the pre-release tree
You can rsync a repo or use a nearby mirror. It's faster if it's on your LAN.
Also make sure you have plenty of hard drive space since the livecd-tools cache lots of stuff.
Pull down the spin-kickstarts repo
git clone git://git.fedorahosted.org/git/spin-kickstarts
Make sure you're on the right branch:
git branch -r # Get a listing git checkout f14 --track origin/F-14 # for example
Edit the repo location
Look in fedora-live-base.ks for this. You'll probably set something like this:
repo --name=fedora --baseurl=http://192.168.0.X/fedora/linux/development/14/$basearch/os
Of course the URL should match the local or remote mirror you're using for this creation task. Make sure you disable any "updates" repo, because you shouldn't need one for the pre-release.
Set your architecture
Do setarch i386 to make sure you're working with the 32-bit architecture, since we want the key to work for everyone.
Make the ISO
livecd-creator -c fedora-livecd-desktop
You may want to put the tmp and cache files somewhere in particular, both are options you can use.
Update the press review sheet
You can find the press review sheets at the following wiki page. They are in Scribus format and you'll need to install the 
scribus
https://fedoraproject.org/wiki/Fedora_press_material#LiveUSB_Review_Sheets
Update all the version numbers. Read the content carefully and be sure to enumerate and describe relevant feature points in the new release. This is only a summary and need not contain lots of detail.