That's not bad for a first try. But it's better to draw something in a way that clearly show's the subject rather then slavishly transferring a picture to pixel art.
For instance with those feet, yes they are probably accurate reduced-size representations of the feet from the frog in the reference picture, but they still look like crap. Better to find a way to draw them so they look like feet and forget about the reference. The same could be said for the pose / angle of the frog itself. That angle at that size is hard to represent clearly with pixels, why not just use another pose that would look cleaner?
Also I have some gripes with the colors. Some of them are just not adding anything at all. Those brown highlights on the back for instance. You can barely see them and they don't contrast well with the skin color.
Don't let my critiques discourage you though, it's not a bad start.