how do I get closer to the metal?

Hello I am final year cs student. I consider myself an average programmer , but I think I can get better. The thing is I never feel I understand what's happening underneath all the abstraction. please tell me in which direction I need to go.
learn assembly
I know assembly but please recommend more books
learn c
I know c. (but we all know "know" is a relative term)
All recommendations are welcome. Please recommend resources.

>>2
obviously I meant metal in a metaphorical sense