May be this sounds muddled, but I think it's important:

1. Code guidelines - formerly I named my vars like a = b * c, instead of more readable employeeSalary = avgSalary * fte, reused a code by copy-paste and did many other bad things in the code. My code was like a mess of unreadable routine. Learning of writing a beautiful code was not easy to me, but as soon as my code was more readable by me and in a team, I understand that I did less bugs. Now I write a beautiful code (thanks to Resharper) easy as one-two-three.

2. Usability and design - usually developers forget about this important thing. But knowledge about it may help to improve programming skills. How? This is fully connected to 'code guidelines' described above. A beauty not only in the code, but in user interface that you develop, has a good influence on developer's happiness, which in turn affects the quality of the code.