Provided that your bird has not damaged it's feather follicles,  there are three important steps that you can take to support new feather growth. The first step is to ensure nutritional, environmental, and emotional wellness.   Interrupting the plucking cycle with a bird  collar has shown good results, as well.  Finally, you'll want to develop and consistently use behavior modification skills including antecedent arrangements, positive reinforcement, and differential reinforcement of alternative behaviors. While it may sound daunting, an excellent resource is  The Feather Plucking Remedies for Birds Workbook.