Today is the feast of St. Thomas Aquinas, Doctor of the Church! Here's Giovanni de Paolo's painting of St. Thomas Aquinas Confounding Averroes:
Here's a passage from De Regno 1.13, in which he lays out the seven essential goals of good government. (My translation.)
Thus taught by divine law, [the king] should set himself especially to study how the many subject to him may live well; which study is divided into the three parts: as the first is to institute a good life in the many subjects, the second to conserve what is instituted, and the third to move what is conserved forward to what is better [conservatam ad meliora promoveat].
And for good life for one man two things are required, one principally, which is acting according to virtue (for virtue is that by which one lives well), the other secondarily and as it were instrumentally, which is sufficiency of bodily goods, whose use is needed to act virtuously. But the unity of that man is caused by nature; while the unity of the many, which is called 'peace', is procured through the industry of the ruler. Therefore for the instituting of good life for the many three things are required.  First of all, that the many be established in the unity of peace.  Second, that the many united by this bond of peace be directed to acting well. For just as a man can do nothing well unless a unity of his parts is presupposed, so a multitude of men, lacking the unity of peace, by fighting among themselves are impeded from acting well.  Third, it requires that through the industry of the rulers there be present a sufficient abundance of things necessary for living well.
So when the good life by the duty of the king is established for the many, it follows that he must set himself to conserving it. But there are three things which do not allow public good to last, of which one arises by nature. The good of the many should not be instituted for only one time, but should in some way be perpetual. Yet men are mortal; they are not able to abide perpetually. Nor, while alive, are they always vigorous, because they are subject to many variations of human life, and thus men are not able to perform their duties equally throughout their whole lives. And another impediment to conserving the common good, proceeding from inside, consists in perversity of will, in that some either are lazy [sunt desides] in performing what the commonweal requires or, beyond this, are noxious to the peace of the multitude, in that by transgressing justice they disturb the peace of others. And the third impediment to conserving the commonweal is caused from outside, in that through the incursion of enemies the peace is dissolved and sometimes it happens that the kingdom or city is scattered.
Therefore to these three a triple charge is placed on the king.  First, that he prepare for the succession and substitution of those who fulfill diverse duties; just as through the divine government of corruptible things, which cannot abide forever, provision is made that through generation one should take the place of another, so that the integrity of the universe is conserved, so also is the study of the king to conserve the good of the many subject to him, in that he concerns himself attentively to fill with others places that are empty.  And second, by his laws and precepts, penalties and rewards, he should force [coerceat] men subject to him away from iniquity and induce them to virtuous works, taking God as example, who gives law to man, favoring those who observe it, repaying with penalty those who transgress it.  Third, a charge is laid on the king to restore safety against enemies to the many subject to him. There would be no use in eliminating internal dangers if one could not defend from external ones.
And then for the instituting of the good of the many there is a third thing belonging to the duty of a king,  that he attentively move it forward, which is done when, in each thing noted before, he studies to perfect it, correcting what is disordered, supplying what is missing, and doing better what he can.