Unlike most here I began learning programming in my late 20s.

On the recommend of my first mentor, the second programming book I picked up was Code Complete by Steve McConnell. It did a LOT to improve the quality of my code, and enable me to write better code.

Be warned that it is a fairly heavy tome. And it is the kind of book which you want to not just read, but to actually absorb into your programming and thinking habits. But if you have the discipline to actually do it, I can't recommend it highly enough.