Follow the Style Guidelines.
When adding a string that will be shown on IRC, always internationalize
it (wrap it in a call to _()).
When making a trivial change to an internationalized string that does not
affect the meaning of the string (typo fix, etc.), please update the
msgid entry in localization file. It helps preserve the translation
without the translator having to review it.
Last rule: you shouldn't add a mandatory dependency. Limnoria does not come with any (besides Python), so please try to keep all dependencies optional.
When you send a pull request, send it to the testing branch. It will be merged to master when it's considered to be stable enough to be supported.
Don't fear that you spam Limnoria by sending many pull requests. According to @ProgVal, it's easier for them to accept pull requests than to cherry-pick everything manually.
Having at least one test case in any non-trivial pull-request is very appreciated.
See also Contributing to Limnoria at Limnoria documentation.