Programming. The first skill one needs to master for being a web developer is programming.

Learning.
Testing.
Basic Knowledge of Design.
SEO.
Understanding Common Security Attacks and How to Prevent Them.
Image Resizing and Effects.
Resoluteness.
Graphic Design. The people who are great at graphic design have a mind for the visual elements that make up a site.
Content Creation.
Platform-Specific Development.
Search Engine Optimization.
Executive Producer.

https://www.davidmeermanscott.com/blog/the-5-essential-skills-required-for-building-an-effective-website