Always provide a log message that accurately describes the purpose of the change.
Avoid writing log messages that are too general. This would happen if you are lazy and go to the top level and check in all files you have been working on for a bunch of reasons.
When fixing a bug from bugzilla, reference the bug number. For example:
"Fixed bug #27, 'unable to run LoadTaxon
'"
While this message doesn't really provide many details, it points to the bug id that should provide a wealth of information about the debugging process.
Try to avoid "fixed typo" log messages. Sometimes, however, that's all that happened :). Which raises another point: test and compile (perl -c) before you check-in.
