In the Lam-Rim teachings there are six methods given to purify karma:

1. reading the profound sutra texts
2. meditating on emptiness
3. reciting powerful special mantras
4. making holy objects such as statues, stupas, and scriptures
5. making offerings to the Guru-Triple Gem
6. reciting the powerful Buddhas - holy names

There are many methods one can use for purification of negative karma.

The practice of Vajrasattva and reciting The Sutra of the Bodhisattvas - Confession of Downfalls are two extremely powerful ways of purifying negative karma and so are important to learn and apply in daily life. These two are unbelievable solutions. Just as one stone can chase away hundreds of birds that cover an entire field, in the same way even practicing either of these two methods just once can purify inconceivable numbers of negative karma.

Multiplying heaviness of bad karma and Purification practices

If one commits just one small negative karma today - for example, killing one tiny Insect - and does not purify that negative action by the end of the day with Vajrasattva practice, then the results of that action will multiply exponentially day by day. After 18 days the negative karma created has become 131,072 times heavier, and as each month and year goes by, the one tiny karma becomes like the size of this earth. By doing Vajrasattva practice, by even just reciting the one-hundred-syllable mantra at least 21 times or the four-syllable mantra at least 28 times, the negative karma is stopped from increasing day by day, month by month, and year by year. Not only does reciting this mantra purify today’s negative karma, but it also purifies the negative karma of past lives. Also by performing the Vajrasattva mantra and practice conjoined with meditating on the four opponent powers, they become perfect and powerful purification practices.

Reciting The Sutra of the Bodhisattvas - Confession of Downfalls is another extremely powerful purification practice in which one recites the names of the 35 Buddhas of Confession. By reciting the names of the different Buddhas, one purifies specific various negative karmas. By reciting the name of just one Buddha, such as that of Guru Shakyamuni Buddha, one purifies the negative karma of 80,000 eons. You can see that this is an extremely powerful practice, especially if you recite the names of the Buddhas while prostrating. Thus, through the practice of these purification practices, you can experience the positive results in this life.