++ for all that fellow monks said above in favor of Source code control, Regression tests and Group ownership of code.
I would add two more items to consider: a Bug tracking system and Peer code reviews.

With all these in place, your average bug's life history goes like this:
- identify and report
- describe how to reproduce and provide a test script that demonstrates it
- diagnose and propose a fix
- implement and test the fix
- run other regression tests
- ask a peer to review your change, explain him/her the problem and how you solved it, and show the tests
- submit the change into the source code control system
- mark the bug as done with

Our game writing good sofware. More often than not our peers help us and we help them. Those few who don't - well, they are missing the best part.

Rudif