Have you ever actually thought about the order in which you put the words - and sense - in a sentence? In In Praise of the Long Sentence I was thinking about how long sentences flow forwards - provide profluence, aka narrative micro-drive - in a way which short sentences can't. But there's also a flexibility about the structure of a long sentence which means you can control the order in which the reader experiences its elements. Narrative takes place in time even more unavoidably than music does, since we don't even have the equivalent of chords, so it's as well to learn to make the most of it. I'm no philologist, but I suspect that English, being virtually uninflected and depending for much of its grammar on auxiliary elements, rather than endings to words, has great advantages when it comes to this. Not for us, for example, the necessity to put the verb at the end.
Thinking aloud, how about this: a not outrageously long sentence with four basic elements, putting forward a fairly simple scenario:
1) I walked into the room and saw that Jim had sat down in the purple armchair, the better to blow his tea cool and talk to Arabella, who had an expression of resigned amusement on her face.
2) Walking into the room I saw that Arabella, with an expression of resigned amusement on her face, was being talked to by Jim, who had sat down in the purple armchair the better to blow his tea cool.
3) Arabella had an expression of resigned amusement on her face, as I saw when I walked into the room, and was talking to Jim, who was blowing his tea cool as he sat in the purple armchair.
4) Jim was sitting down in the purple armchair and talking to Arabella, who had an expression of resigned amusement on her face while she watched him blowing his tea cool, as I saw when I walked into the room.
5) The resigned amusement on Arabella's face, as I saw when I walked into the room, was caused by watching Jim sitting in the purple armchair blowing his tea cool and talking to her.
6) Talking to Arabella, who had an expression of resigned amusement on her face as I saw when I walked into the room, and blowing his tea cool, was Jim, who was sitting in the purple armchair.
7) Sitting in the purple armchair and talking to Arabella was Jim, blowing his tea cool, and I saw when I walked into the room that she had an expression of resigned amusement on her face.
8) Blowing his tea cool as he sat in the purple armchair was Jim, and I saw as I walked into the room that he was talking to Arabella, who had an expression of resigned amusement on her face.
Now, of course they vary enormously in how clear and/or euphonious they are, and not only because I've just knocked them out in five minutes. Some even mean subtly different things. I'm fairly confident there aren't any actually grammar or syntactical incorrectnesses in there, though there may be slight ambiguities in the less felicitous ones, while if James and Arabella were the same gender, there'd be scope for pronoun trouble. And then of course there's the real horror which crops up astonishingly often in the work of bad and beginner writers straining for elegant variation; the inevitable result of straining is that they suffer a dangling participle first, and then several other medico-literary ailments:
9) Sitting in the purple armchair I saw Jim, who was blowing his tea cool, and the resigned amusement on Arabella's face as he talked to her which I saw when I walked into the room.
So, once you've done enough of this kind of five-finger-exercise to feel confident and begin to think about the possibilities, how do you choose? Well, a good basic principle is to stick with the order in which your view-point-character perceives things, which is likely to be 1) in this example. 4) is an example of what I call 'zig-zagging', which starts a little way in and then jumps back to the beginning. It's usually an attempt to put the most striking bit first, and then fill in the backstory: it's easy to do, and easy to do badly, and it can be the death of profluence, killing narrative drive just as having to go back home to get the picnic can kill a day at Kew Gardens. Zigzags often happen because the writer is thinking in that order: picnic first, then - oops - we need to supply the goods to make it happen, so it's very understandable, and exactly the kind of thing which revising is for.
Of course your viewpoint may be that of a knowledgeable narrator, not a character, but it's not really different: you're still seeking to control the order in which the reader perceives the elements of the scene. It might be 2) if you've just had a run of sentences with a simple subject--main-verb--object structure - elegant variation is not always a bad thing, because a run of the same rhythm can make your prose sound, well, plodding. I have a characteristic sentence structure, into which I fall when I'm tired or have a cold, and I'm sure you do too. Fortunately reading aloud picks it up with embarrasing clarity, even if you have got a cold.
Then there's the matter of how easy it is to understand. It's hard, when you play with sentences for a living, to read things as if you don't. I know that some readers found the balanced, formal, often antithetical structures of Stephen's voice in The Mathematics of Love hard to get into, while others absolutely loved it. It was central to the distinction between his voice and Anna's, but I paid the penalty in blog reviews. So be it. I absolutely love sentences which, if you like, are syntactically complex in separating auxiliaries from their main words and nesting phrases inside other phrases, but yet on inspection turn out to be grammatically quite simple, and one reason is that the rhythm's often so much better. Mind you, this taste does mean that on a bad-cold day I'm liable to commit 6).
There's also a question of voice: the shape and rhythm of the sentence should be suitable to the character (in both senses) of the narrative, but so should the thinking, the sequence of ideas or observation. Would your narrator take more notice of Jim or Arabella? Would s/he observe their emotion along with their action, as in 5), or only after a general survey of the room, as in 1)? This may be about context, being rooted in this moment in the plot, or may be about character.
I suppose it would put a lot of aspiring writers off to start a course and be issued with five-finger exercises. But The Art of Fiction has plenty, and maybe we could all do with more of them. No, it's probably not essential, especially if you read widely and attentively, and are blessed with a writing mind like blotting paper. But there's a limit to what techniques you can learn while writing creatively, just as there's a limit to how well you can refine your backhand if you only ever play matches. And the more you do refine each stroke, the more likely it is that just the right strokes will happen, just when you need it, in just the right order.