Though I did some sprite art last year, I'm certainly no expert. From my experience and the advice I read online back when I was spriting, however, you just have to try out different pixel placements when working on parts of an image. For the closed eyes in the in-thought emotion, for example, try making the lines for the eyes less curved, see how that looks, try making them more curved, try moving the whole line up, down, right, left, etc. I'm afraid there is no strict logic when it comes to sprite art, as least not as far as I'm aware of; it's a practice makes perfect kind of thing. It does seem like you're on the right track, so keep it up!
I hope this advice helps you out. Good luck with the project!