As part of any purification practice we use the "Four Opponent Powers." These are (sometimes translated differently and I have even seen them placed in a different order) Regret, Reliance, Resolve, and Remedy.
Regret: we contemplate and generate genuine regret (not guilt) for all negative actions we have created
Reliance: we seek refuge in three jewels, not only for our benefit/protection, but so we may one day work perfectly for the benefit of others
Resolve: we make a determination (or vow) not to create particular negative acts (a determined interval of time can be included) --here you might formally pledge not to eat meat etc...
Remedy: prayer, recitation, or practice intended to purify the negative actions.