The layout is the hard part
A skin is a flat texture wrapped onto a model. The output follows the classic 64 by 64 template.
Describe clothes, not poses
Say what the character wears and its colours. Pose and body shape come from the game.
Simple reads better in game
Skins are seen at a small size. Two or three strong colours beat fine detail.
FAQ
What file do I get?
A PNG in the classic skin layout. Upload it in your game profile.
Does it support the slim model?
The output targets the classic layout. Slim arms may need a small manual edit.
Can I use it on a server?
Yes. It is your file, generated on your credits.