Unless I've missed something (which is entirely possible), you can't use the Advanced Workflows to trigger changes to other fields within the same item that the trigger initiates from. There only seems to be support for field changes in other items..?
ie. A category field labelled 'Status' gets changed and we would like a progress bar within the same item to be automatically adjusted based on the 'Status' field. For example: 'Status > First contact' sets progress bar to 5%, 'Status > Quoted' sets progress bar to 25%, 'Status > Complete' sets progress bar to 100% etc.