Find a mantra that you can relate to and say it everytime a judgemental thought creeps into your mind. Repeat your mantra over and over until the thought is gone. As you disrupt the pattern of your thought again and again, you will find that that particular genre of thought will come to you less and less. Dont feed your negative thoughts by allowing them room to grow. Ignore them by repeating your mantra -- while they may never disappear entirely, they will at least be short lived.