I finally got around to developing my first APEX Plugin!
To summarize this plugin is a code syntax highlighter based on http://alexgorbatchev.com/SyntaxHighlighter/.
. This is the same syntax highlighter for code samples on this site. You can download it here: http://www.apex-plugin.com/oracle-apex-plugins/item-plugin/syntax-highlighter.html.
Keep it simple. Chose a simple feature to add. If you decide to add something very complex you may just get lost.
Put your PL/SQL code in a package/function so that you can develop using a 3rd party tool such as Toad or SQL Developer. This will allow you to quickly debug your code. Once it’s working you can extract it and put it inline with your plugin
Look at other examples. View other plugins and see how they were built etc.