This type of meditation is called Japa meditation and called repetitive prayer. You can do this in a formal way, sitting in meditation or informally anywhere and anytime. It can be done as a chant, aloud or silently or it can be imprinted by other means (see notes). Don't be too quick to dismiss its effectiveness. Just watch how the chanting at a sporting event fires everyone up.

1. Choose a word that means something to you - a quality you want to encourage like peace or joy. Or choose the name of a deity. It could be a mystical symbol, a special combination of letters or a poem. Make it something that you want to imprint. Make it joyful and uplifting.
2. Repeat your chosen word either silently in your mind, aloud in a whisper or usual speaking voice, or you can sing it. Many people use prayer beads or rosaries or malas to count repetitions. Move each bead along as you chant the mantra and repeat until you get to the end.
3. Get a feel for the energy of your chosen mantra and allow this energy to grow in you as you chant. Let yourself be changed by it. When your mind wanders off (and it will), bring it back where you left off and continue. And if you have an agile enough mind to repeat the mantra in the back of your mind while thinking about other things, try saying it aloud. There's no right or wrong way to do this. It is just a simple, joyful practice.
4. If you are doing this informally, take your mala on the bus with you as you commute or as you wait in line. Some people keep a small mala on their wrist for on-the-spot meditations. When frustrated at the office or while waiting in line at the post office, chant a peaceful mantra to help restore your balance.
5. Many people practice this type of meditation in between and alongside their everyday activities. This makes daily life a steady flow of prayer.
6. Group chanting can multiply the effects of mantra meditation. You can either get a group together to chant or bring a chant to an existing group or religious gathering. But you are not limited. Don't forget that there are thousands of people in the world who practice this type of meditation using words or ideals that match your own. So each time you practice, you are already meditating with others.
7. Continue until you have worked through all the beads on the rosary or as long as you like.

If you really become interested in auditory mantras, you may want to become aware of how certain tones can affect certain parts of the body. The science of it is huge.

Chanting is not the only way mantras can be imprinted. Carving mantras onto rocks is a widespread practice in some parts of the world. And Bart Simpson does it another way every episode, when he writes 'lines' on the blackboard.

There are no right or wrong ways to do a meditation. The instructions are guidelines; adapt them to who you are and to your needs at that particular time. Be curious about the process itself.

Remember most meditations become richer the more you practice them. They reveal more of themselves. It can take practice to remember to do a meditation when you need to, and it can take practice to go through the steps. But that's why it is called practice, and for most of us, we practice for the rest of our lives.