I used to have an unhealthy fear of drawing fingers. I completely avoided any picture showing these tricky appendages. My early attempts turned into deformed, misshapen looking claws without much detail.
If you take a close look at fingers, they are full of wrinkles, creases, recesses, and indentations. Even young fingers!
My trials and errors have taught me that to make a convincing finger, you must adhere to light and shadow. Pay close attention to where the highlights hit the wrinkles and creases. Where the deepest shadows are in the valleys.
The key is contrast, contrast, contrast.