Web design and development. User interfaces in static HTML and CSS or with dynamic CMS
Search engine optimisation, google analytics with keyword suggestions.
Mobile first design, everyone is on mobile, over half web traffic is mobile.
Google just announced that page speed will be a ranking factor in SEO. People leave after 5 second load times.
Unity game engine, 2d and 3d games. I've made 2D 3D games, and augmented reality apps.
PHP, edit theme, build sites from scratch. Most popular CMS, makes it easier to manage your websites.