How can someone demonstrate their competency and skills to help them get a job?

• A software developer could prove and validate their skills posting or contributing to an open source project on github.
• A technical writer could help write the documentation for open source projects on github proving their technical comprehension.
• A writer could provide a huge list of links to their work.
• A writer could participate in a group writing project.
• People could add links to their linked in profile to previous jobs and projects.