Extending workflow with workflow add-ons
There are a number of very useful add-ons that will provide additional components such as conditions, validators, and post functions. The following list presents some of the most popular workflow-related plugins.
JIRA Suite Utilities
You can find a number of very useful conditions, validators, and post functions with this add-on. For example, the Update Issue Field post function that ships with JIRA allows you to update any issue fields such as priority and assignee when a workflow transition completes. The JIRA Suite Utilities plugin complements this by providing a very similar Update Issue Custom Field post function, which handles custom fields. There are many other useful components such as the Copy Value From Other Field post function, which will allow you to implement some amazing logic with your workflow. A must-have add-on for any JIRA. You can find out more at https://marketplace.atlassian.com/plugins/com.googlecode.jira-suite-utilities.