I dont think there was any one I could point too as 'the' one. I think I learned mainly just by trial and error, and just straight perserverance. The interface I couldnt get my head round at first, and I dont really think theres any tutorial (that I know of) that made that easier. personally I think it's mostly a case of just putting in the hours and it just starts to feel more and more familiar and less and less like it wants to ruin your mind.
I sometimes think having books in hard copy is better than online tutorials which you turn on and off, and Eric Keller and Scott Spencer both have quite good books on ZBrush. But id say, like, with your trapjaw model, just import that into Zbrush and start playing. When you get to a point when you're not sure what to do, or you want to do something but dont know how...look it up... I think that would be good as if you follow a tutorial you'll end up making something which you otherwise might not have chosen to model...?? And because youve already invested time into your trapjaw model, thatll make what you do that little bit more intuitive.