To be clear what I am talking about see the image below. It has nice Settings link which leads to plugin settings  from plugin list.

Why I think this is important? Usually plugin creates new submenu in Settings, but sometimes it uses different name and it is not easy to find one. In case 20+ plugins are installed, which is a real case, it is not easy to remember where all these settings are stored.

I consider Settings link  as a must have thing when developing plugin and its pretty easy to add it, see below

Probably in your plugin you already added setup page through add_submenu_page function.

Next thing is to add Settings menu to plugin page:

add_filter(
   'plugin_action_links_' . plugin_basename(__FILE__),  
   'wp_action_links' 
);

function wp_action_links($links) {
   $settings_link = '<a href="' . menu_page_url('plugin_setup', false) . '">'. esc_html(__('Settings')) . '</a>';
   array_unshift($links, $settings_link);
   return $links;
}

Voila!