Ask HN: Widget Development

I'm looking to begin developing a widget for others to embed on their site. As it is, it will just be a stand-alone widget (not a WP plugin or Drupal Module). I've been trying to do some searches for getting started, and best practices however, I have been coming up a bit thin. Was curious if anyone could give me some tips, examples from work, or resources to take a look at. Any and anything is greatly appreciated.