What is best practice for tying in grounds on a metal box?
This is where copper crimp connectors come in handy.



Lets say you have a 3 gang box, with three cables entering, and three devices to connect.  You also have to bond the grounding conductor to the box, if you're using a metal box. So you might have three grounding conductors entering, but need 4 grounding conductors, and they all have to be bonded.

Leave the grounding conductors from the three entering cables long, and get a scrap piece of bare wire to use as a pig tail.  Feed the three grounding conductors through the crimp connector, so that there is enough wire left to connect to the devices.  Insert one end of the scrap piece of wire into the connector, then crimp the connector.



Now tuck the crimped grounds back in the box, and attach the bonding wire to the box (using either a screw or ground clip).  Attach one grounding conductor to each device, and you're done.

Alternatively, you can leave one conductor really long (while still including the extra bonding conductor), then use that single conductor to connect all the devices.