I'm going to make a guess here but... I am assuming you normally draw from life, right? Judging from what you've uploaded, this appears to be the case. If so, then I'd like to note that when drawing, you shouldn't think about what you're drawing as shapes or forms (or even objects). Instead, think of them as sources of reflections and sources of light. I know this probably sounds a little strange, but getting into this mode of thinking early on in your drawing career can be extremely helpful later on, when you find that you're capable of capturing forms very accurately, but feel that something is 'missing' from what you're drawing (or painting or what have you). Incidentally, speed sketching is a great way to practice this mindset, since it ensures that you won't be able to capture the form of what you're drawing, and forces you to focus on its essence instead. Go ahead and give it a shot (the mindset, not necessarily the speed sketching, though I do recommend trying it at least once) and please post back what you come up with. I look forward to seeing your work.