"Just for today, I will not worry" is taught in Reiki as one of the five precepts.
This precept teaches us not to worry or to let go. There can be several explanations of what it actually means but right now I do not intend entering into its academic definition. I would restrict myself to what this precept implies.
Worries are the result of our unfulfilled needs and desires which are endless. There are innumerable needs that keep you worried nearly constantly. The only thing that varies is the nature and degree of worry. Constant worry taxes the nervous system, keeps the mind preoccupied and reduces the productive ability. Worry and contemplation are two different things. Planning for something and then putting in the effort does not mean worry in the typical sense. Contemplation is a sign of wisdom that leads to logic, discoveries and understanding of realities while worry is an expression of dissatisfaction with your present, with what you have. Worrying over an issue does not solve the problem while contemplation does lead to solutions.
Worries can be minimized by being content. Sit down quietly to think over, analyze your desires and needs, keep the genuine and cut out the non-essentials. A mere reminder of the precept might be of very little help but if you back it up with your whole-hearted effort, trust the Creator and yourself, you would see your life much better than ever before. Just believe that whatever is coming to you from Divine is for your good anyway. Such positive changes at the conscious level will begin to generate the vibrations of higher frequency, which lead to mental satisfaction and better quality of life. With conscious effort, one can train the mind to carry out the assignments, achieve the goals, perform day-to-day functions and yet remain free of worries. This is what this precept teaches. Almost all religions of the world teach contentment and trust in the Creator. So, it could be a good idea to learn more about your religion and practice those teachings as well. In addition to that, regular self-treatment with Reiki also helps in naturally becoming more realistic, calm and relaxed. Try it if haven’t done it before, because as they say, Reiki is more about experiencing and getting to know what it can do.