Sometimes we need some quiet time a few decibels lower than a full blown Kirtan. Japa meditation is personal chanting of a mantra.
One of the most powerful mantras is known as the maha-mantra:
Hare Kṛṣṇa Hare Kṛṣṇa
Kṛṣṇa Kṛṣṇa Hare Hare
Hare Rāma Hare Rāma
Rāma Rāma Hare Hare*
Japa meditation has many benefits: Peace of mind, knowledge of the self, happiness, freedom, and ever-increasing love. It is recommended you chant the mantra at least 108 times (this constitutes one round and is usually counted on beads) and increase as you are able. Aim for 16 rounds a day and you will feel immense benefit in your daily life, internally and externally.
*Kṛṣṇa sounds similar to Krishna.
Here are some links to help you learn and improve your japa meditation:
2. Japa group