the way i started was to just jump in. It supports MSVS 2005 and fuckin rolls straight away, so it's not much of a learning curve. There are ~ 17 tutorials on the site, and they are grouped very well. I suggest you start trying to solve them and you are bound to find some interesting shit under a few stones therein. =)
My second step was to read the
Pro Ogre 3d Development book from Apress which filled in a few of the holes and helped me unlearn a lot of things from HL2 Development.
I have my first tutorial coming out for Ogre, and i am going to release it in video form as well as an article on my wiki. Should be pretty interesting, but all n all its been a very gratifying experience. I have to get back to recording. =) Get yourselves ready for the crazy antics. I hope you guys enjoy what you see, i sure as fuck have!