For prose, I tend to use the concept of "flow" rather than rhythm. It's not dancers or music, it's a creek flowing over rocks, smooth here and foamy there and gently burbling here and splashing there and roaring for just a moment, but the seemingly-random changes should be pleasing.
In my opinion, flow in prose can't be judged on just one sentence--a very large part of it is the way that the sentences interact with one another, and in fact often the way that the paragraphs interact with one another.
I rarely worry about anything like flow until I'm working with at least three or four paragraphs, and quite often I don't think about it until I'm dealing with an entire scene or other logical block of writing.
First, I write the sentences primarily for content--it's not as if I don't care at all about how the sentences are crafted, but I do force myself to let the sentences come out with minimal tweaking (that is, minimal tweaking for style; there may be a lot of tweaking for meaning) in the moment. I reassure myself, repeatedly, that I'll be coming back to that awkward phrase or that sentence that seems like maybe it should come earlier.
Then I sweep through with a preliminary cleanup. I fix awkward or redundant phrasing, I replace "good enough" words with that word that was teasing my brain but that I couldn't find while forcing the sentence out, I combine paragraphs or add paragraph breaks. I often move sentences or blocks of sentences up or down. If there's dialogue, I fix any voice issues--that character wouldn't use that word, that character wouldn't speak in a sentence of that complexity. I tighten the dialogue--we didn't need that exchange; a simple nod would have accomplished the same thing.
Only then do I have a chunk of prose that's fairly complete in meaning and message, and ready to be tweaked for pure language issues.
I start with sentence variety and (it suddenly occurs to me) tense. If he blahed, he blahed, and he blahed, I find a different way to put two out of three of those. If there's a lot of past continuous tense, I try to shift most of it to simple past. If I have several simple sentences, I may make some of them more complex sentences, separated by the surviving simple ones. If I have a lot of complex sentences, the reverse. I read through it and read through it--in my head; my primary focus is how it sounds in my head, not aloud--and in the end I'm just making changes that "sound better" to me, and it's purely a judgement call. At some point, I'm dead to it and I have to come back later.
One way that I can tell that each sentence depends on its surrounding sentences is that when I add or remove a sentence, I almost always have to reshuffle its neighbors a bit.