You can use wood chips soaked in water that are put in the charcoal fire if you are using a charcoal grill. Put them in the smoker box if you are using a gas grill. Either will add a smoky flavour to your ribs. When you place the rack on the grill make sure the ribs do not overlay the fire or they will burn.
Set your grill to a low temperature and cook your ribs for several hours. You want your grill at around 225 F/110 C for the whole cooking time, check on your grill with a thermometer to make sure.
If you are using wood chips, add more every hour. This is mainly important for the first 2 hours. After 4 to 5 hours your ribs become tender and the meat becomes loose around the bones.
You can pre-cook the rack by either boiling the ribs for about 30 minutes or by placing them in a slow cooker. Once you are ready to grill, season the ribs and cook them indirectly until done. The disadvantage of this is that you can literally boil out the flavour of the meat and the ribs will not absorb the flavour of the smoke as well.