These six properties (dhātus/elements) are means of escape. Which six?
"Furthermore, there is the case where a monk might say, 'Although compassion has been developed, pursued, handed the reins and taken as a basis, given a grounding, steadied, consolidated, and well-undertaken by me as my awareness-release, still viciousness keeps overpowering my mind.' He should be told, 'Don't say that. You shouldn't speak in that way. Don't misrepresent the Blessed One, for it's not right to misrepresent the Blessed One, and the Blessed One wouldn't say that. It's impossible, there is no way that — when compassion has been developed, pursued, handed the reins and taken as a basis, given a grounding, steadied, consolidated, and well-undertaken as an awareness-release — viciousness would still keep overpowering the mind. That possibility doesn't exist, for this is the escape from viciousness: compassion as an awareness-release.' (AN 6.13)
Karuna (compassion). See also Brahmavihara.
As a factor leading to liberation: AN 6.13
Systematic practice of ~: SN 42.8
Practicing ~ as a way to deal with annoying people: AN 5.161
Detachment and Compassion in Early Buddhism (Harris)
It's not possible to develop compassion, understand it even, if one is after certain elements, follwer of certain dhatus, holding on wrong views and disregard the tripple gems. Such are no means. So fist real refuge is generally the only refuge.
Such answers like
Compassion is the willingness or wish to help others therefore I suppose compassion can only be practised when others need help when it is obviously they want help.
might give foundation for defilements to regard there ideas for right, but such does not cover what is called skillful or path contuctive.
The wish to help other beings has nothing to do if one is actually able or not, regardless of lack in oneself or by handicaps of others: boundless, meaning that all beings are to be included.
Of course such as to develope karuna requires such as compassion or pity toward one self first. This requires the understanding that one actually need to be helped, misses certain things for having no kind of suffering.
If one does not see dukkha, one does not see ground for help. Not knowing dukkha in one self, not spoken about the cause, how can one develop even desire to help other?
There is no being that is not subject to suffering, knowing it or not.
To be able to develope conductive compassion it is required to have right view, without right view, the following parts of the eightfold path, which are in fact deeds of compassion, starting with virtue outwardly, can not come into be.
Developing right compassion, even to expand it torward all beings is therefore not possible for a wordily mind, person, but might be so fare, "just" a training.
One who is a disciple of the noble ones — thus devoid of greed, devoid of ill will, undeluded, alert, & resolute — keeps pervading the first direction [the east] — as well as the second direction, the third, & the fourth — with an awareness imbued with compassion. Thus he keeps pervading above, below, & all around, everywhere & in every respect the all-encompassing cosmos with an awareness imbued with good will: abundant, expansive, immeasurable, free from hostility, free from ill will.
Such is impossible for a person with giant ego, totally overestimating one self. Such a person will of course, guided by his defilements, prefer to dwell in his "emptiness" (e.g. in his ignorance).
At least, one IS able to help every being - to pull away the ground of such foolish ideas: even if one might not see certain lack, does not know certain mind, in keeping precepts, being without intention to harm, has threefold rght intention, one helps all beings.
"There is the case where a disciple of the noble ones, abandoning the taking of life/taking what is not given/illicit sex/lying/use of intoxicants, abstains from taking life. In doing so, he gives freedom from danger, freedom from animosity, freedom from oppression to limitless numbers of beings. In giving freedom from danger, freedom from animosity, freedom from oppression to limitless numbers of beings, he gains a share in limitless freedom from danger, freedom from animosity, and freedom from oppression. This is the first gift, the first great gift — original, long-standing, traditional, ancient, unadulterated, unadulterated from the beginning — that is not open to suspicion, will never be open to suspicion, and is unfaulted by knowledgeable contemplatives & brahmans... (AN 8.39)
Taken on such on high level, this is by the way the reason why monks and certain brahmans are often adressed as "lord of compassion", because of the gift of virtue and then the other trainings and for teaching possible the way to end suffering.
So compassion in action on the eightfold path helps actually every being, and ideas, like even favored by deluded minds here, giving cause to be corrected for those able to see through defilements, have no rightous ground at all.
Since this is actually a place that gives much reason to face the suffering of beings, caught in wrong views, here is planty place to spread compassion, pity for them, since that grave hopeless situation no one can directly posible help, is indeed a field that "cries" for compassion and may lead later to righous equanimity "beings are heirs of their kamma", that's then dwellingin emptiness, not possible to gain without having done the right deeds in body, speech and mind befor.
So the matter in short, incl. act-ually all being:
And how does one, when watching after oneself, watch after others? Through pursuing [the practice: e.g. stating with developing right view by practicing silas], through developing it, through devoting oneself to it. This is how one, when watching after oneself, watches after others.
"And how does one, when watching after others, watch after oneself? Through endurance, through harmlessness, and through a mind of kindness & sympathy (e.g. developing a mind, thoughs of compssion). This is how one, when watching after others, watches after oneself. (BaMboo-acrobats)
So, right here where this is, there is, at the point of a wordling, no better act of compassion as to strive for right view by practicing generosity, precepts and reflecting the Dhamma and let go of certain ego-trips:
Abandoning the wrong factors of the path
"One tries to abandon wrong view & to enter into right view: This is one's right effort...
"One tries to abandon wrong resolve & to enter into right resolve: This is one's right effort...
"One tries to abandon wrong speech & to enter into right speech: This is one's right effort...
"One tries to abandon wrong action & to enter into right action: This is one's right effort...
"One tries to abandon wrong livelihood & to enter into right livelihood: This is one's right effort."
— MN 117
Cultivating skillful ways of thought
"And how is one made pure in three ways by mental action? There is the case where a certain person is not covetous. He does not covet the belongings of others, thinking, 'O, that what belongs to others would be mine!' He bears no ill will and is not corrupt in the resolves of his heart. [He thinks,] 'May these beings be free from animosity, free from oppression, free from trouble, and may they look after themselves with ease!' He has right view and is not warped in the way he sees things: 'There is what is given, what is offered, what is sacrificed. There are fruits & results of good & bad actions. There is this world & the next world. There is mother & father. There are spontaneously reborn beings; there are brahmans & contemplatives who, faring rightly & practicing rightly, proclaim this world & the next after having directly known & realized it for themselves.' This is how one is made pure in three ways by mental action."
— AN 10.176
With much karuna! (and mudita) and as a "Bodhisatta" once explained: "How few understand what love (goodwill & compassion) really is,... : Wisdom and the work for it.
Sabbe sattā sabba-dukkhā pamuccantu.
May all living beings be freed from all stress & pain.
For those more interested in how to develop the Brahma Viharas: The Sublime Attitudes: A Study Guide on the Brahmaviharas
Beware of the manifold extrems of Mohayana-Compassion, leading to pain for many and oneself in wandering on, feeding on the "beloved"...
[Note: This is a gift of Dhamma and not meant for commercial purpose or other low wordily gains by means of trade and exchange.]