How to work for liberating ALL living beings?

1) Apart from generally showing compassion and benevolence towards all living beings, in what ways do accomplished Buddhism practitioners work for the liberation of living being as diverse as, say, ants, pine trees, salmon and e-coli bacteria? What do the scriptures say, and what do the more recent writings say on this matter?

Even in the traditional Mahayana systems, not all living things are sentient, (else why would the traditional formulation even include the word?) True, some versions of Mahayana Buddhism incorporate "nature", including trees and rocks. This, but I'm looking for a better reference about the status of trees and rocks.

2) How do accomplished Buddhism practitioners liberate from dukkha the beings of non-earthly nature of other lokas, such as angry deities and hungry ghosts? What do the scriptures say, and what does recent literature say?

Kṣitigarbha is an Bodhisattva (portrayed as an ordinary looking monk) who rescues people in the hells. Depending on the flavor of Mahayana Buddhism, this is either meant literally, or it is a story about what behavior that a Bodhisattva practicioner should emulate. (Scholar Jan Nattier in "A Few Good Men", where she notes, "After paying homage to the Tathagata at the entrance to the vihara, the bodhisattva is told to remind himself that "I, too, should become one who is worthy of this kind of worship""-- i.e. capital-B Bodhisattva's like Ksitigarbha are to be copied, not so much adored & petitioned for help. (This isn't true for all of subsequent Mahayana!)

His greatest compassionate Vow being: "If I do not go to the hell to help the suffering beings there, who else will go? ... if the hells are not empty I will not become a Buddha. Only when all living beings have been saved, will I attain Bodhi." ref: Buddhanet

The story of Ullambana is about merit a son whose mother has become a hungry ghosts. He holds vegetarian feasts for monks, and then some percent of the merit accrues to his mother so that she can exit that realm.

I think Buddhists went through periods of reification of metaphors and de-reifications of metaphors. When sutras swing towards talking about sunyata/emptiness and the way our mind shapes our experience, then the heavens and hells are in our heads, metaphors for states of mind. And then next chapter they are reified again and people are taking the consequences of these stories very seriously. If there really are hells, it is our responsibility as Bodhisattvas to do something about it.

Interestingly, often the "doing something about it" was deferred to the next life time. Ancient Buddhists were called upon to care for the sick, sometimes called on to give to the poor, particularly beggars, but the bulk of the good deeds done would be done in the next life. In modern times, we're starting to see Humanistic Buddhism and Engaged Buddhism, so while I don't know how effective it is, some Buddhists have their heart in the right place when it comes to dealing with people who are in the metaphorical hells at the moment.

This answer is based on Theravada. so it may not appropriate here, comparing with Andrei's answer.

As per the "Maha Hasthipadopama Sutra in a paragraph", you liberate 'Your Self' by attaining direct realization that in fact there are no any such "sentient beings" to talk about. "Sentient being" is only a nominal designation. Two keywords to study are anatta (sanskt., anatman) and shunyata.

Now, as a practice of paramitas (of generosity, forbearance, renunciation, loving-kindness, and equanimity + 4), the commitment to staying in samsara and deferring one's own liberation until all sentient beings attain nirvana, requires complete surrendering of one's antipathy to samsara and craving for peace, complete surrendering of one's ego - which (the surrendering) paradoxically becomes the gate to Realization.(by removing the lock of it)

From The Maha Hasthipadopama Sutra

“Friends, just as when a space is enclosed by timber and creepers, grass, and clay, it comes to be termed just ‘house,’ so too, when a space is enclosed by bones and sinews, flesh and skin, it comes to be termed just ‘material form.’

“If, friends, internally the eye is intact but no external forms come into its range, and there is no corresponding conscious engagement, then there is no manifestation of the corresponding section of consciousness. If internally the eye is intact and external forms come into its range, but there is no corresponding conscious engagement, then there is no manifestation of the corresponding section of consciousness. But when internally the eye is intact and external forms come into its range and there is the corresponding conscious engagement, then there is the manifestation of the corresponding section of consciousness.

“The material form in what has thus come to be is included in the material form aggregate affected by clinging. The feeling in what has thus come to be is included in the feeling aggregate affected by clinging. The perception in what has thus come to be is included in the perception aggregate affected by clinging. The formations in what has thus come to be are included in the formations aggregate affected by clinging. The consciousness in what has thus come to be is included in the consciousness aggregate affected by clinging.

He understands thus: ‘This, indeed, is how there comes to be the inclusion, gathering, and amassing of things into these five aggregates affected by clinging.

Now this has been said by the Blessed One:

“One who sees dependent origination sees the Dhamma; one who sees the Dhamma sees dependent origination.”

And these five aggregates affected by clinging are dependently arisen. The desire, indulgence, inclination, and holding based on these five aggregates affected by clinging is the origin of suffering. The removal of desire and lust, the abandonment of desire and lust for these five aggregates affected by clinging is the cessation of suffering.’

At that point too, friends, much has been done by that bhikkhu.