So here in Bellingham WA, I've started a new GM inventive. When my GM's run a society scenario, I will reward them with a 1 dollar gift certificate from our sponsoring game store, Eagles Games. I started this with the month of April and gave out 25 bucks. We are a small store and just started running three tables on both Sunday and Monday. I'm trying to spread out the GM time so no one person will get burned out.
As of this time I have 10 GM's that I have in the GM pool. I have started some of these GM's with quests. From there they start with easy scenarios, that I will sit in as a player. After the game I give them pointers, and we do this for their first three games. I don't always have to sit in on all the games, a lot of the GM's pick it up quickly.
After passing out the bucks, all the GM's told me they wanted more behind the screen time and I had two players ask how they could join the GM pool.
Other things I've done is having a private pizza party for GM's, run GM only scenarios, that I will not put into the scenario rotation, and now I'm going to start a Monday afternoon campaign, with GM's getting first choice at the table.
I have a few other ideas, but I was wondering what others are doing in their stores.