A few tips:
- Don't ever save a sprite as a .jpg if you can help it. That's a format that easily destroys the quality of pixelart of any kind.
- Unless you're going for a realistic look (which usually isn't the case with pokemon), then outlines should be of a significantly darker color than the other colors of a sprite. I'm looking at the skitty, in this case.
Your customs are fairly decent, though they suffer from having a few stray white spots, and by not having an outline that goes all around the sprite (the minka's tail). The other sprites could use some work...I think the main things wrong with them have been mentioned already.