Give the Publisher One MS at a Time

I have a completed manuscript under consideration at the third place I've sent it. Since I have been shopping the ms around, I have completed another one. My question is; what is the proper way to begin sending out the second manuscript? Do I send it to the publisher that has my first? Do I begin again at the beginning of my list of LDS publishers? Thanks for your help.
--Querying

Do not send a second manuscript to a publisher who is still considering your first.

Everyone else is fair game. You may send it to anyone who has seen and rejected the first one, or to anyone else on your list—the order is up to you.