According to Stuart Mckelvie, a good Salesforce developer must be curious. You must be highly inquisitive about what goes on around you, the latest Salesforce technique and technology. New Salesforce applications are released more than two times a year. They come with new APIs, new features and new methods so you must stay on top of the new trend so that you won't become an obsolete developer. Study the new features before you use them. You can learn more on blogs, YouTube and ebooks.