Having been raised Jewish, I had no familiarity with a rosary until I began to study Hinduism, where it is called a mala or a japa mala. In Buddhism, they are known as juzu or nenju. A mala generally has 108 beads, an auspicious number in Hinduism and Buddhism. The use of a mala or rosary is quite effective for meditation.
For each bead, you say a mantra, prayer, or a thought upon which to meditate. The rosary allows you to rid yourself of notions of time. You are not meditating to a clock-time, or to a count, you allow the rosary to set the time for you. When you reach the head bead or fringe, you are finished.
Holding your rosary in your dominant hand, grasp the first bead between your thumb and middle finger. Take a deep breath, let it out, and say your mantra. Use your forefinger to move to the next bead, and repeat the process.
I have lately been experimenting with using specifically Wiccan phrases instead of Sanskrit mantras. Certainly you can use Om or Om Shanti Shanti Shanti. But try one of these (from The Charge):
My Law is Love Unto All Beings.
All acts of Love and Pleasure are My Rituals.
I have been with you from the beginning, and I am that which is attained at the end of desire.
