Tips - 4.x

References

Configuring Workflow - basics on how to configure a workflow so you can take advantage of the features of this add-on
Advanced Workflow Configuration - know the difference between conditions, validators, and post functions

Test your workflow!

Workflows can be complicated. Define a reasonable test scenario for your workflow on a test project or test system. Often, it is the only way to find errors before putting your workflow in production.

Errors

Post functions are run after the transition has already occurred - there is no turning back. If your post function has configuration errors, the JIRA server log is the only place those will be reported. When testing and debugging your workflow configuration, make sure you have access to the log and ensure your changes have not introduced unnoticed errors. If necessary, follow Retrieve problem determination information - 4.3 and above.

Using JQL

The JQL support provides some powerful conditioning and substitution support. Test your JQL in interactive JIRA first. If you use substitution variables for the JQL, double quote values that may (on substitution) contain blanks.

Custom fields not changing

Ensure the custom field is defined for the issue type you have
Ensure it is on the supported Custom field types when using set. Use one of the copy custom fields instead if appropriate. Otherwise, open an issue to get support for unsupported types.
Retrieve problem determination information - 4.3 and above