When releasing a new WordPress Plugin, the wordpress.org’s Codex page on Plugins is definitely a good place to start. Be sure to read Writing a Plugin.

Let’s say, the hard part is done, you’ve coded the plugin and tested it and removed all bugs, you could find by you own. What’s next? Here is a list of things to do I can come up with:

• Host your Plugin on WordPress.org. As soon as you know, you’re going to release your WordPress Plugin to the public, register at the wordpress.org’s plugin repository if you haven’t done so and add you plugin. It might take a few days before Matt Mullenweg gets back to you, and your SVN repository is ready. Read this book.
• Take your time to do a propper readme.txt. The readme.txt file of you plugin is parsed, when the wordpress.org’s Plugin repository is scanned.
• Do Screenshots. According to the readme.txt’s standards (markdown syntax), you can add screenshots to you plugin, and you should. Especially if your plugin is an administration feature and/or you do not have a demo online.
• Internationalize. You should definitely prepare your plugin for this. If you do so one day, you might be surprised by another WordPress user, sending you an email containing translation files, you couldn’t have done by yourself!
• Create a Plugin Homepage. This can be a page on your blog with an easy to remember permalink. Update this page whenever you release a new version of your plugin. Set the download link to the one that is offered by wordpress.org, this saves you bandwidth.
• Announce your Plugin. Tell the other WordPress users, that there is a brand new plugin.
  • create a post on your blog
  • Register with an post about it on the weblogtoolscollection forum
  • also post a message on the wordpress forum
• Update other Plugin Databases. Since WordPress.org has got it’s own plugin repository, there are only 2 databases still on the net afaik:
  • http://wp-plugins.net
  • http://wordpress.softplug.net

  Register and enter your plugin’s information.

• Fix Bugs Quickly. Once released, people might immediately post problems tha ran into on the comments section of you plugin’s page. React on that reports asap.

Am I missing something? Please add to the list with you comments, I’ll update the post!