At WordCamp Milwaukee 2015 I talked about building better themes. We talked about theme design, theme development standards, coding best practices, Retina and responsive styling, and theme optimization.
Check out my slides, or the starter theme, Regolith, on GitHub.
I gave a talk at WordCamp Minneapolis 2015 about building functionality plugins. We talked about the difference between themes and plugins, and what should go in each. I covered getting setup for writing a plugin, best practices for WordPress development, and gave some real world examples of plugin functionality.