The hardest part of WP plugin/theme development is learning how hooks and filters work. Once you've got those down, you get can get wild.

Some great starter plugin resources (in order of my personal preferences for style and organization):

  * https://github.com/DevinVinson/WordPress-Plugin-Boilerplate

  * https://github.com/hlashbrooke/WordPress-Plugin-Template

  * https://github.com/mattyza/starter-plugin

https://developer.wordpress.org/ really has everything you need. Examples, best practices, function documentation, etc.

If you really want to learn you should find a problem you have and solve it by building a plugin. Practice makes perfect.