One of the things I notice is that the arms don't seem to have elbows in the first drawing, but to be fair, I've been drawing since childhood and only in the past couple of years figured that mess out. Repitition is everything, and eventually you will sort out what you do and don't like about your art and will do little things differently each time. I could be lame and say draw from life and you will learn, but everyone uses that advice, so instead I'm just going to say draw whatever you'd like, and draw it a lot, and have passion in it.
Sometimes you'll feel like drawing is rough and frustrating, but that's totally normal and doesn't mean that you don't love it. Just remember where your passion is and keep up even when you don't like it. In the wise words of I think Adventure Time: "Sucking at something is the first step to being kinda good at something."