To make a smoke bomb start by placing about 1/2 cup of damp, but not wet, wood chips on a piece of foil. Wrap the wood chips so that one side has a single layer of foil. Poke several holes through the foil to let the smoke out. I'm using two smoke bombs, but you can use more if you wish.
Place the smoke bombs under the cooking grate as close as possible to the burner you are using. You will need to preheat the grill hot enough to get the combustion of the wood started. Once you see smoke coming out of the smoke bombs, turn down the heat and place the ribs on the grill.