Ill will is one of the 5 hindrances to clear thought described by the Buddha. In SN 46.51, the Buddha describes it’s feeding and starving. It is fed by improper perception of harshness. It is starved by frequent proper attention to the heart’s release by love. But what love? I recommend developing love of freedom from ill will. This can be based on another love (love of yourself, the Buddha, some other being) or on a desire for total freedom from suffering. This love is self sustaining, the more you carefully feed it, the better it feels.
Let’s say you are trying this out but you’re not sure how to do it. First pay attention to your starting point. For the sake of this example, I’ll assume desire for total freedom from suffering is the starting point because it’s what I have experience with. Great basis for virtues btw. Out of a desire for total freedom for suffering, create love for yourself. After you have a charge of love going, feel the freedom of heart that the love provides and use it to destroy ill will. Focus on the freedom of heart and breathe in a way that makes it spread. Once you have seen the way that the freedom of heart that comes from love evaporates ill will, develop love of freedom from ill will based on the knowledge you have seen for yourself, based on love of yourself based on desire for total freedom from suffering. Now you’re not done with this after a time. You need to do this regularly. Freedom from ill will requires care and feeding.
How can you recognize ill will? Ill will is tight. Ill will leaks corrosive material. Ill will seeks harm. Ill will makes it hard to think pleasant thoughts. Ill will can be partly earth element, it can manifest as crystal capsules filled with hate that radiate harmfulness and inspire clinging. These are the things to look out for, of course you know how simple ill will feels.
Let’s say someone says something displeasing. Out of love for yourself, recognize that a painful feeling has entered through ear consciousness, and try to limit the repurcussions. You may have ways of perceiving that try to auto activate that produce ill will. You want to flood them with love of freedom from ill will to destroy the ill will as fast as it is created, next develop desire to modify that mode of perception without harming it. next, concentrate your energy for the purpose of modifying the perception, next adjust your mind to be conducive to modifying that perception, finally gather together the right kind of investigation to modify that perception. Next repeat “may all beings be skillfully happy.” When you do this, use the investigation to see how to influence the perception toward freedom from ill will. At this time be on the lookout for grasping and clinging that perpetuates ill will. If you see them, reflect, “where this (grasping or clinging) is, this sort of suffering is (aim the “this”es appropriately, the suffering is the existence of ill will, and the destruction it causes, as well as the loss of ability to think pleasant thoughts. Then reflect “from the arising of this comes the arising of that (or this) suffering.” Then reflect “where this sort of clinging (or grasping) is not, that (or this) form of suffering is not.” Finally reflect “From the cessation of this (grasping/clinging) comes the cessation of that form of suffering. You want to improve the existing grasping and clinging so that it no longer allows modes of perception that feed ill will. If the grasping/clinging goes away entirely, that’s ok too. If you want, you can think of this as a complicated step one for MN 20