Begin the Jupiter mantra on a Thursday (the day ruled by Jupiter), during a waxing phase of the Moon. The ideal time of day to chant a planetary mantra is in the early morning, when all is quiet.
Mantras can be started at any time, however it is best not to start within three days on either side of the dark Moon (New Moon). If possible, start when the Moon is bright and waxing. Some prefer to start mantras on the day ruled by the planet. This is not critical, but for those who want, you may start the Jupiter mantra on a Thursday.
How to Chant the Jupiter Mantra
Chant the Jupiter (Brihaspati) mantra 19,000 times. This need not be done in all one sitting. See the Planetary Mantras page for how prayer beads help with counting, and for more tips.
Pronunciation
Deva-nancha rishee-nancha gurum-kanchana saneebam boodee bootam treelo-keysham tam na-mamee brihas-pateem.
I bow down to Brihaspati, god of the planet Jupiter. He is the spiritual master of all the demigods and sages. His complexion is golden and he is full of intelligence. He is the controlling lord of all three worlds.
English translation
Why it Works
The Jupiter mantra can be seen as a type of prayer that invokes the grace of a planetary energy to lessen its negative effects as revealed in the horoscope.
There are many kinds of astrological mantras. Some are devotional, some are Vedic, and some are Tantric. The mantras given here are mainly devotional. Therefore, while one should be careful to try and pronounce the mantras as accurately as possible, they will still work with individual pronunciations.
For more on how planetary mantras work, see the Planetary Mantras page.