I'm not really good in giving critique, but I'll do my best!
For one, the right arm looks crooked. I'm not saying that it should be straight, because it will look weird. For example:
See how unnatural it looks? If you want to make the arm look a little curved, check out how Elesa's arm looks like here:
[IMG]
It's curved, but not too much. It's straight, but it's a little curved. You might want to practice more on curves and lines, too, just to improve more. Speaking of straights and curves, the strap of the bag is too curvy and the lines are too ... messy? Most bag straps I've seen are straight (but not perfectly straight, like the first example!). See Brendan's sprite as a reference.
[IMG]
The pants are okay, but they could use a little bit of erasing, y'know what I mean? The left eye is also not seen much.
As for the shoes ... I don't really know, honestly. Whenever I edit a trainer sprite, I usually just copy + paste shoes from other trainers and tweak them a little. You could also use some shading. I've edited your sprite in a few places so that you can understand what I mean:
[IMG]
(I failed on the arm, too :P)
Just remember, I started from nothing. I began spriting without any kind of professional knowledge. I'm just a Pokemon fan who wanted to edit things, and I've had my practice. Just keep trying and you'll get there, okay? I see loads of potential in you; don't give up on pixel art!
P.S. Sorry if I didn't teach you much. XD