There are three steps to (electrical) heaven.
1.) scrape off all dirt in the area of the point where you want to do the electrical ground point
2.) use sand paper and wipe off the old paint until you find really good shiny bare metal. To keep the unavoidable rust off use the same zinc rich paint as you would use to do electrical point welding. Leave the zinc paint dry over night to be sure it is really dry.
3.) Bolt the stuff together as shown in the diagram. Use the tooth lock washer between the freshly painted area and the future electrical ground contact. Be aware, that the teeth of the washer grips into the electrical connection and the zinc paint.
Just as easy as that.
It is easy to get a good ground contact but it is a bit of looking forward to keep this good connection.
I think best is, after connecting the cables to put petroleum jelly all over it, especially in the gap where the locking washer is. So, the oxygen cannot get into contact with our connection, and therefore the metal of the electrical contacts keep shiny as new.
I used stainless steel bolts to bolt all this together. Again a point to avoid oxidation.
MGOC Member: A6421-3