For me, flow just takes practice. The more I write the more cadence appears. However, my somewhat incomplete English skill-set also held me back. Until I knew all the ways to use modifying phrases, going beyond the mere addition of simple subordinate clauses to the beginning or end of the sentence, adding to my repertoire the ability to chain modifiers into more complex sentences, I was unable to create suitably artistic sentences to express my ideas*.

*Sorry about the self-indulgent sentence.

One thing I have noticed in my writing group is that, with a good cadence, an author can write a sentence of fifty or sixty words and no one will bat an eye, while a thirty word sentence with a weak cadence will unfavorably affect readers. For instance, the first paragraph of Joseph Heller's Something Happened as a ~80 (I tried to count it but my phone rang in the middle) word sentence which just flies by.