One idea I ran across was from a video I watched on Teaching Channel. The teacher tells her class not to interrupt unless it is one of the 3 B's: burning, barfing or bleeding. You can check out her video HERE.
I recently made this poster to hang close to where I do reading groups. Students can see it and hopefully be reminded that they don't need to bother me during reading groups unless it is something really important like one of the 3 B's. (you can grab a copy by clicking on the picture)
I also wear a purple necklace (like the one pictured below) that I picked up at our local dollar store. I got 5 of the necklaces for $1. My students know that if I have the necklace on, they are not to interrupt the reading group.
We are now on our second week of reading groups/centers and a handful of my little firsties are still working on not interrupting.
I would love to hear ideas that work in your classroom that help minimize interruptions.