The following items can help your Nintex workflows run more reliably and efficiently:

1. Disable Nintex history logging in the workflow settings

2. Create one Nintex database per Web application in SharePoint

3. Run the Nintex purge workflow script every six months or more often, depending on your farm

https://community.nintex.com/docs/DOC-1218

4. Use workflow constants.

Best Practice for Workflow Design – Using Workflow Constants

5. Define a good backup and restore for Nintex workflow.

NINTEX WORKFLOW BACKUP AND RESTORE OVERVIEW (PDF)