I am passionate about writing good code, and I'll try to offer some practical advice. As others said, the first step is understanding the importance of writing clean code and taking pride in your craft. By doing this, you are already ahead of most other programmers who don't really care. Now, how do you improve?
1) Read books.
With 4-5 years of experience, you already have a good intuition for "good" and "bad" code. Still, it doesn't hurt to learn more about it. There are a lot of good books on this subject.
The first is "Clean Code", by Robert C. Martin. It's the first book I read on this subject, and I learned a lot. Note that the book uses Java in the examples, but I think the ideas would apply to most other languages.
Its author, Uncle Bob ( http://en.wikipedia.org/wiki/Robert_Cecil_Martin ) has long been a proponent of writing clean, beautiful code. He recently did an interview for Xebia: http://blog.xebia.fr/2011/05/25/interview-avec-robert-martin... (French blog, but the interview is in English). In it, he advises:
"Well there are a number of books that talk about writing code well. Kent Beck wrote a book called “Implementation Patterns” very recently. It’s an excellent book all about software craftsmanship. The pragmatic programmers wrote a wonderful book in 2000 called “The pragmatic programmer”, again a wonderful book. Chad Fowler wrote a book call the “Passionate Programmer”. Again the book is about doing everything well. I wrote a book recently called “Clean Code” which is very specific about particular things you can do with your code to do it well. So there is a tremendous number of resources that are available for people who are interested in doing software craftsmanship well."
Out of those, disregard "The passionate Programmer". It's an okay book, but its focus is on building a good programmer career, not on code.
"Implementation Patterns" by Kent Beck is a great book with a lot of best practices when writing * Java * code. Less useful if you use another language.
"The pragmatic programmer" is a good book on software craftsmanship. I'm personally half-way through. There is a lot of good advice in it, but I often find myself thinking it's "common-sense". Maybe because I've already been exposed to most of the ideas by reading blogs? Still, it's a great book, with a lot of best practices. It's main focus is not code, though, so you might want to start with other books if your focus is on writing good code.
To these books, I'd add "Code Complete (2nd Edition)" (language-agnostic) and "Effective Java 2nd Edition" if you use Java.
Summary:
If you use Java, read:
- Clean Code - http://www.amazon.com/Clean-Code-Handbook-Software-Craftsmanship/dp/0132350882
- Effective Java 2nd Edition - http://www.amazon.com/Effective-Java-2nd-Joshua-Bloch/dp/0321356683
- Implementation Patterns - http://www.amazon.com/Implementation-Patterns-Kent-Beck/dp/0321413091
- Code Complete / Pragmatic Programmer
If you use another language, read:
- Clean Code - http://www.amazon.com/Clean-Code-Handbook-Software-Craftsmanship/dp/0132350882
- Code Complete - http://www.amazon.com/Code-Complete-Practical-Handbook-Construction/dp/0735619670
- Pragmatic Programmer - http://www.amazon.com/Pragmatic-Programmer-Journeyman-Master/dp/020161622X
Other people might chime in with suggestions for other languages?
2) Practice.
Implement what you learned in the books. Keep improving.
3) Read other people's code.
Read good open source code. Not all code is good code. Ask around for OSS projects with good code in your language.
If you use Java, start with:
- Google Guava - http://code.google.com/p/guava-libraries/
- Google Guice - http://code.google.com/p/google-guice/
- Spring Framework - http://www.springsource.org/
4) Practice.
5) Practice.