Your designs should be creative and original
many suits of colors help the design stand out
the design of clothing choice can be whatever you like, just make sure the design isn't so bland and unoriginal.
add some extra details like scars, patterns, or secondary limbs etc.
The more complex the design is, the more recognizable and creative it is.
Make sure your design isn't too close like your other OC's or it would be a loop of the same thing over and over.
If its furry, anthropomorphic etc.
I would highly recommend using a underrated unpopular animal as your main animal of the OC.
You choose what it is.
the more unique and animal that people hardly use the more its going to be recognizable.