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Write down some ideas/notes before you actually create the Pokémon. Something like the type of animal it's based on, the habitat it lives in and how it adapted to it, and how it differentiates itself from other Pokémon in terms of stats and abilities. Anything that'll help you remove any worthless designs on the Pokémon is good.
Pic related, for example, is everything you SHOULDN'T do. Too many patterns, too many spikes, too many parts that add nothing to the design. It just looks cluttered and messy.
I'm tired. I hope you can make sense of everything I wrote.