Joe,
As TiddlyTweeter mentioned, The Tinka plugin is quite helpful making plugins.
Something to keep in mind;
Plugins are a package that once installed needs you to save and reload, they can be disabled and present shadow tiddlers that can be overwritten, you can delete these overwritten tiddlers and revert to the plugin version, all quite nice. But a point I would like to make is you can package any tiddlers in a plugin and they do not need to include java script, they could just provide macros, data tiddlers, or simple tiddlers.
There is a separate set of issues about creating plugins that include javascript and or javascript libraries. This requires more technical information.
Regards
Tony