I just discovered that u did the very first skin on PMC. GG !

I think, to improve yourself, you should :

1) Improve the shading,

a) I mean, if you want to do a green shirt, don't go for a dark green to a light green, but rather go from a dark blue to a light yellow/green. It also mean, don't have only 4 colors in your shading, but more like 6 or 8, and if you have 1 or 2 shading on all your skin, you could even have 10 colors. There are examples :

1) b) You can also, change the "intensity", light is in poor intensity and dark is really intense, (it's a parametre in paint.net, you should use it for chosing your colors, then going to a skin editor).

1) c) Also, don't worry to go from a really dark color to a really light one, when you start doing skins, you always have a very little shading, but you can do more.

1) d) And you can play with these parametres to do all types of textures.

2) You could play more with the second layer, 64x64 (maybe you didn't in this case because you began from an old skin, done 10 years ago when there was not the second layer)

3) You could also impove the realism of the forms of your skin. I mean that :



I really exagerated to show you, and the second layer could help you make the forms a bit more interesting.