Prose cadence has mostly to do with making the emphasis in a sentence fall on the most important words:
But, in a larger sense, we can not dedicate—we can not consecrate—we can not hallow—this ground. The brave men, living and dead, who struggled here, have consecrated it, far above our poor power to add or detract. The world will little note, nor long remember what we say here, but it can never forget what they did here. It is for us the living, rather, to be dedicated here to the unfinished work which they who fought here have thus far so nobly advanced. It is rather for us to be here dedicated to the great task remaining before us—that from these honored dead we take increased devotion to that cause for which they gave the last full measure of devotion—that we here highly resolve that these dead shall not have died in vain—that this nation, under God, shall have a new birth of freedom—and that government of the people, by the people, for the people, shall not perish from the earth.
Notice how the first sentence is arranged to throw the emphasis on the words dedicate, consecrate, and hallow, but also to emphasise "we can not" through repetition. And in the last sentence we have the emphasis on "God" "freedom" and and then "people", "people", "people". That is prose cadence.
A sentence with good prose cadence tends to say what you are expecting it to say. It leads you to its desired conclusion by the way the emphasis falls. This means that you can also use prose cadence to surprise, to lead the reader to expect one thing and deliver another.
Prose cadence is not about making your prose sound poetic, thought that can sometimes be the effect. It is about conforming the shape of the sentence to its sentiment. Poetic rhythm is always overt. Prose cadence often goes unnoticed, even when it effect is profound.
I think in these matters, it is not a simple matter of principles vs ear. We can certainly pull out great examples of prose cadence and analyse what is going on, but that analytical skill probably will not translate into practice all that well. I think is really comes down to attuning your ear to the sound of great prose -- which means reading the great prose masters attentively. In your actual writing you will write by ear, but that ear can be trained by deliberate and attentive practice and reading.