Requirements for Vetted Plugins
Vetted plugins should work well out of the box, and should autoconf correctly in most cases. The Concise guide to plugin authoring describes a plugins methods autoconf and suggest.
Their graph should be significant and easy to comprehend. See the Guide for good plugin graphs.
POD Style documentation in the plugin (or a separate file named <PLUGIN_NAME>.pod)
Vetted plugins shouldn't conflict with plugins in other packages as well (ie: plugins in munin-node or munin-plugins-extra).
These plugins can go in $(DESTDIR)/usr/share/munin/plugins.