My input, and I could be totally wrong, but this looks a bit rushed through the steps trying to get to the result. If you don't already, before getting into the studies proper, take ten minutes and a piece of scrap paper (anything will do), and practice ellipses, circles, straight lines, c- and s-curves. Vary lengths, direction, etc. If you're not familiar with the concept of "ghosting" lines, look it up, (proko's drawing basics is a fantastic resource). In terms of what's there, it looks like a view from below, so I'd expect to see more of the underside of the jaw and the connection to the neck tube. At each set of stages, (he breaks down the steps into logical groups that make sense), pause and reflect on what you've done, correct anything that looks off before moving on. As we build on top of prior steps, if the early one's aren't right, the later ones won't be either. Good luck and keep practising! Several shorter studies with reflection between/after are better than one long one.