That may be because you're not that bad at it.

Well this is good, but ummmm, you know you don't have to draw so big. Best method that helped me were a bunch of little doodles that focused on design and body shape. Just try a rough go at what's in your imagination and don't stop until you get what you want or hit something better. For example,
http://krudetoons.deviantart.com/ar.....kson-421996628 Darwin (the one on the left) was really an accident while I was trying a go at various dog like characters (Brian, Courage, etc) a few years back. One the other hand,
http://krudetoons.deviantart.com/ar.....ster-421952331 Guster started out as a lose idea for a sad yet lovable label dodging loner and I just sort of drew him around thatl premise and improved him throughout the years. So basically what I'm saying is, don't be afraid to experiment and "wing it" sometimes. Try other people's styles, but also try a style you envision and not just what you think will look passable. It may seem like a dead end at first, but as time moves on you'll start to see what I mean.