Your prayers may not stop you from speaking subsequent words that are negative, but it will correct the previous words that you have spoken over your life. The temptation to speak negative words will always be there. It is going to be a battle. Even when Jesus was tempted, the Bible says the devil left him for a little season. The devil took a break, with the desire to come back again and continue to wage a war of temptation against the life of Jesus (Matthew 4:11).
Friends, it is going to be a battle. But as you continue to abide in the place of speaking the right words, you will prevail.
The temptation to speak contrary to scriptural prescription may be there. But your decision is what is going to help you. You have to make a decision, Lord, from today, I will not speak negatively anymore. And as you make that decision, God supplies the grace for you to continue to walk in it.