The Law of Attraction states that "like attracts like." Popular sayings such as "what goes around comes around" and "you reap what you sow" explain the function of the Law of Attraction. Also called the Law of Cause and Effect, this law is the basic explanation of karma.
All of life is made from energy. Energy vibrates at various frequencies; your thoughts, feelings and attitudes determine your current frequency, or state of being. No matter whether the frequency is a high one or a low one, you attract things of like frequency to yourself. So make those thoughts good ones!
Knowing this, it makes sense to maintain, as much as possible, the frequency that matches the things you desire. This is done by experiencing the feeling of having it already. As you feel that excitement or exhilaration of having it, your creative energy attracts more things matching this frequency, and your physical world will change to match your high vibration.
Remember that the Law of Attraction works whether you know you are using it or not.