Most of the times, when I have to draw for someone else, I don't feel so self confident about my skills, I barelly could know if poses as request some people are allright or if how I draw fits with their expectations.
Awesome work! You don't need to be down on yourself, it's just going to take lots and lots of practice. When you start doing requests, make them be VERY specific, that way if it doesn't turn on out they want, it doesn't end up being your fault! Your an awesome artist!