Mike, there is another choice. Just run the tooling surface of the leather quickly under a faucet.
My dad did full-on leather carving (not tooling) for years. He was quite good at it. The method above is what he taught me. Yes, you keep an eye on the leather color and feel, and re-wet when it starts to dry. Too dry, and the tooling doesn't want to take. Too wet and it is soggy and stretches, and sometimes also doesn't take as well.
As James suggested, you need to play with it a bit to get a feel for it. Also, if stamping, keep in mind that large stamps need much more force than small stamps. Be cautious too if using a small stamp not to cut through thin leather with too much force.
I am still learning all of this, so it is good to get solid advice.
God Bless, Marc