Making an intention into a dedication is sending your energy outward. Sometimes this is not what you need. Sometimes what you really need is to draw energy inward. This can be done through an invocation. Invoking resources and support from outside ourselves is a common way to begin a yoga practice.
Invocations can be as simple as chanting “Om” once or thrice, and allowing the vibration to fill the body, and then linger. Longer chants can also be nice. Chanting is a wonderful form of pranayama, which not only stimulates energy to flow through us, but also has a calming, centering effect on the mind. Ashtangis use the vande-gurunam invocation.
Many students recite chants from the growing amount of kirtan music available on CDs today, such as those by Deva Premal or Wah! and all the various Das brothers.  Deva has a couple of lovely versions of the Gayatri mantra, an invocation of the solar energy, which is recited daily in many India families.
Not all invocations need to be chanted; you can invoke whatever symbols or energies you relate to. Simply ask in your mind for their support, strength, guidance, or whatever it is you feel you need right now. Your practice is your payment in return for this boon.