What defines a professional developer? The initiative „Clean Code Developer“ (german only, english version using Google Translate) tries to facilitate a common understanding of this question. It has started to collect principles, rules and best practices for better software.
They see as basic principle for becoming a professional developer to be self-conscious about your work and always try to improve yourself as well as to adhere to some common best practices and working principles. Trying to lead developers to more professionalism, they have also collected a lot of concrete recommendations for the day to day work. To make it easier to follow these practices and rules, all recommendations are grouped by a so-called grade system. So you can start with the easy ones and get to the maybe not so easy to follow rules later.
Even if you don’t agree to all suggested practices and principles, the side is definitely worth a read since you will find a lot of good practices concentrated on one location. Additionally, they also maintain a link list for useful tools and frameworks.
You can find the Clean Code Developer initiative here.