Before you open a ticket or send a pull request, search for previous discussions about the same feature or issue. Add to the earlier ticket if you find one.
Create your own fork of contrib where you can make your changes.
Make sure you have Node.js and the grunt cli installed. Then install contrib's development dependencies with npm install.
Make your code changes, ensuring they adhere to the same coding style as Underscore. Do not edit the files in dist/.
Make any necessary updates to the qUnit tests found in test/. Run grunt test to catch any test failures or lint issues. You can also use grunt watch:test to get instant feedback each time you save a file.
Make any necessary documentation updates in docs/. Do not edit index.html directly.
After updating the docs, run grunt tocdoc to rebuild the index.html file. Visually inspect index.html in your browser to ensure the generated docs look nice.
Send a pull request to documentcloud/underscore-contrib for feedback.
If modifications are necessary, make the changes and rerun grunt test or grunt tocdoc as needed.
And hopefully your pull request will be merged by the core team! :-)