You want thin blue smoke. While I don't have any good explanation on the chemical differences between 'blue' smoke and white smoke, there's certainly some advantage in taste. Blue smoke is a slightly cooler smolder from the wood, rather than an almost-burning-state.
Use chunks of smoke-wood (roughly fist-sized chunks, rather than the coin-sized chips of wood) for long-smoked BBQ. Put the smoke-wood on first, put the cover on and let the smoke-wood get down to a smolder before you put your meat on.
However - it is a fairly minor difference. I've made plenty of good BBQ with the wrong-kind of smoke when the food when on. If you're just starting-out, don't freak-out too much that your smoke isn't perfect. You'll have your hands full trying to keep it within your target cooking temperatures, which is more important!