A clearly-articulated if somewhat Ruby-centric and dated ("now do svn diff") explanation of how to contribute a patch to an open source project.
- Snoop around
Load up the project into your editor and poke around.
If it has test cases (!) try running them. You may need to create some databases and/or modify the Rakefile/connection details to work with your database. Hopefully the project comes with rake tasks to create/drop the databases. rake -T should find them.