first you have to find a good reference. Then you have to observe how the light works on the object.
You can also look on how others artist resolve this problem.
1- define your shape
4- highlight and reflected light
I'm starting to wonder if I should go the Half Minute Hero route with my game. The character's main weapon is logistically way too strong. So I can't really let the player continuously grow it.... But if they had to build it up each time like HMH, that could work. Also it lets me take advantage of my randomly generated maps so much more. Hmm... This could work!