I ensure that the fire is burning nice and hot. I normally start off with one load of lump and then add a few logs. After that, I add wood as needed - usually a log or two per hour. As long as the fie is burning hot the smoke will be fresh. I find that adding chunks to charcoal causes more undesirable smoke than burning logs, as the chunks have a tendency to smolder rather than burn clean.
Equipment - Poor Man's Jambo aka Jumbo, Weber Kettle, Weber Smokey Joe, XPS Gasser