Good coding style and practices.

The most important thing, as other Monks have already mentioned, is to make sure your code functions properly over a well-specified range of operating conditions. This is achieved by creating a good test suite.

One of the next things to consider is style, which can:

• Make your code more robust
• Make your code easier for you to understand
• Make your code easier for others to understand
• Establish your reputation as a professional

You could do worse than to read the book, Perl Best Practices.