Make a list of negative behavior you will be ignoring and a list of positive behaviors you can acknowledge and praise students for engaging in. For instance, you might choose to ignore non-threatening or inappropriate talking, the inability to sit still and random noise-making while praising students for sitting up straight, engaging in their work appropriately and getting along with other children.
Set an audible timer, such as an alarm clock or cooking timer, to go off at random intervals during class. You can play with the timing, but once or twice throughout each lesson is a good place to start.
Pause your lesson when the timer sounds and praise students who have been behaving well while ignoring those who have been behaving poorly. This will reinforce the idea that engaging in improper behavior will no longer net the child any attention, but that acting positively will.