You're In Trouble Now, Mister!

Jaron is 9 months old and is in the stage the doctors call "exploring his world". (I think it is more like being ornery, but what do I know, I am just the mom.)

While Jaron is a very active baby, and while we do encourage discovery, we also realize that the time is nearing for appropriate discipline. The hubs and I have ideas of how we want to go about this for older children, but when it comes to this age we are a bit lost. We like the idea of having the discipline fit the crime (when possible), but that doesn't really work for someone who can't sit still for more than 1.2 seconds.

I am looking for wisdom you seasoned moms might share with this young, inexperienced mom.

What is appropriate discipline for a 9 to 12 month old? (Or is there even such a thing?)
When did you start discipling your child(ren)?
What works? What doesn't work?

I am very interested to hear your thoughts.