The lab farm run is intended to get as many trick or treat bags as possible.

To do this it is very important that you tag as many enemies as possible and also do as little damage as possible!
Reason: Little damage means more players can tag and therefore more players receive loot.

You also want to increase your magic find stat as much as possible.
More magic find means more trick or treat bags.

A great way to prepare for the farm run can be found on this site:
Fast-Farming Community[fast.farming-community.eu]

A more detailed visual explanation - also about further increasing magic find during the run - can be found in the video below.