One of the National Association of Colleges and Employers (NACE)'s core Career Readiness competencies is Professionalism/Work Ethic:

"Demonstrate personal accountability and effective work habits, e.g., punctuality, working productively with others, and time workload management, and understand the impact of non-verbal communication on professional work image. The individual demonstrates integrity and ethical behavior, acts responsibly with the interests of the larger community in mind, and is able to learn from his/her mistakes." 

A positive professional image tells employers that you are reliable, responsible, and committed to improvement by accepting feedback and seeking out help when you need it. You demonstrate professionalism through your attire, responsible behavior, and appropriate communication—both face-to-face and online. Building your professional image begins with self-reflection.

Create Your Professional Image

• Read A Guide to Professionalism in the Workplace.
• Commit to improvement by accepting feedback and seeking out assistance when you need help.
• Call your own phone number to make sure your voicemail and ringtone sound professional. If you haven’t already done so, consider changing your primary email to something generic such as firstname.lastname@gmail.com.
• Create and maintain an appropriate online presence:
  • Google yourself to see what others see when they search for you. Check to see what appears on social media sites such as Facebook and Instagram. Always ask yourself: Would I want a future boss to see this?
  • Bury your digital dirt. If there are some questionable links that pop up, you’ll want to create new material that will cover it up. Consider joining LinkedIn, a professional networking site, or consider setting up a professional blog to develop a clean online presence.
  • Build a web presence in your field. Follow blogs that are related to your career interests or professional association (a group of individuals in similar professions), or join an email distribution list, or listserv, that matches your interests. Search the web to find a professional association that is right for you.
• Request letters of recommendation from any advisors, faculty, group leaders, or previous employers who could speak positively about your professionalism, leadership, or abilities.