I have a Geshi plugin for Moodle 2.x.
http://moodle.org/mod/forum/discuss.php?d=176780
It just sits there, but I'd like to clean it up and make it easier for others to install it.
Any best practices?
This would be a good place to start:
I would also suggest making the code avaiable on github. In that forum post you mentioned something about file hierachy? You can make it repo that others can possible insert into their own codebase as a git submodule. See how other projects release their blocks/plugins on github (for example: https://github.com/lsuits/quickmail).
If your plugin needs core changes, then you can put that in your README file. However, in Moodle 2.4 there is activity in making it easier to add in plugins to the TinyMCE editor.