I find this ratio to work for me. From Amazingribs.com :
"How much is enough? It is best to weigh the amount of wood you use so you can increase or decrease it as you wish in future cooks. The amount you need will vary depending on your preferences, how tight your cooker is, they type of fuel, the thickness of the meat, and if you use chunks, chips, or pellets. Pellets are especially good for measured amounts.
Here's where to start your experiments: On charcoal, use no more than 8 ounces by weight of wood for ribs. Use no more than 16 ounces for pulled pork and brisket, and no more than 4 ounces for turkey and chicken. Add it in doses. Put on about two ounces when you put on the meat and add another two ounces when you can no longer see smoke. On gas grills, double the amount. "