Practice 20

Nice work! If you're wondering about wrinkles in clothing, I would suggest popping by some fashion websites or advertisements. They usually have a slinky girl in loose, wrinkly clothing in them.

www.americanapparel.net/ American Apparel is pretty good because they don't retouch their models
www.hm.com/ca/subdepartment/LA… ((Plus there's always good style ideas to steal if you wnat your characters to be trendy )
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This woman is wearing a dress, not shorts, but you can see the top.

Higher end fashion brands like Chanel or Gucci can be inspiring, but they usually retouch their images a LOT, so they can be unreliable for studying art.