Winter Month: 2 
Day 
This isn't a complex guide, just something you should maybe read :3
Might help your designs sell.
Or might make you mad at me.
Not saying you hafta follow this.
Theme
Some unnatural designs often go after a theme. Food themes are popular, especially for the closed species you see around deviantart. Some examples are weather themes, animal themes, etc.
Colors
Highlighter designs, or designs that literally look like they've been dipped in rainbow llama vomit, are quite often seen in Adoptables. Adoptables are breedable(usually) designs that are usually more simple can have two designs that are strikingly similar. WolfPlay, along with many similar SIM games should have atleast a few wolves that look the exact same :p I bet my life on that. Your designs on Wolfplay technically belong to the artist who made the markings. Kind of. The ones born and generated by birth anyways. I think lol don't trust me.
Highlighter designs are flashy. And although some people like them, it kinda takes the creativity away.
Usually.