What you need to do is a "dry run", just burning enough charcoal to maintain a temperature of around 225°F. If your smoker doesn't have a thermometer built into it, you'll need to get one of those probes that can go into an oven and hooks up to a digital readout.
Once you know about how much charcoal it will take, and learn how much charcoal to add at given intervels to maintain that temperature, the dry run is over.
When you are ready to smoke something, soak your wood chips in water for 20 minutes before smoking. Get the fire going. When the chips are ready, get a piece of aluminum foil about 2' long. Place a handful of chips on one end of the foil, then wrap the foil up so it forms a packet of chips, with a couple layers of foil between the chips the exterior of the packet. Puncture a couple holes into each side of the packet. Lay this packet on the charcoal, then place your meat onto the smoker.
I could usually get about 30 - 45 minutes of smoke from a packet of chips.
I have since switched to Hickory chunks with oak logs for fuel, and rarely use charcoal for anything except getting the fire started. You might want to try using Hickory chunks as well. Soal them for 30 - 45 minutes before use. A good-sized chunk will provide smoke for about 45 minutes.
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Eat Meat and Save the Plants!