1- naming the plugin
2 - readme.txt
http://wordpress.ord/extend/plugins/about/readme.txt
http://sudarmuthu.com/wordpress/wp-readme
http://wordpress.ord/extend/plugins/about/validator
http://daringfireball.net/projects/markdown/syntax
3 - Plugin header
https://codex.wordpress.org/File_Header
4 - Actions
https://codex.wordpress.org/Plugin_API/Action_Reference
5 - Filters
https://codex.wordpress.org/Plugin_API/Filter_Reference
6 - Shortcode API
http://codex.wordpress.org/Shortcode_API
7 - Wordpress Settingss API
http://codex.wordpress.org/Settings_API
http://codex.wordpress.org/Function_Reference/register_setting