Writing long sentences is easy. Doing it well is hard. In most situations, an idea told briefly carries more force than one told lengthily. Most technical writing should remain brief when possible. But, in some creative situations, there’s opportunity to break from the short sentence.
No minimum word count exists for the long sentence. You can tell this is a short sentence. And, given a basic understanding of English syntax, you can tell that this sentence, while grammatically correct, is longer (though no more informative). A good long sentence does not simply add more clauses and asides than a shorter sentence. To write a good long sentence, one must grasp not only structure, grammar, voice, and syntax, but the artistic movement of an idea and the lyrical rhythm of language. Take, for example:
It was a small classroom and a bright day, and he sat at his high seat before a black chalkboard while his pupils marched into the room and to their seats surrounded on all sides by the peach white of the plaster walls.
The first part (It was a small classroom and a bright day) introduces the setting. The phrase is simple, though begins with zeugma—a small rhetorical trick, which, in this case, uses It to refer to both the classroom and the day. The next clause introduces the protagonist and how he sees himself. His seat is not literally high, but his position, compared to the rest of the class, is. Color influences the mood as well: the black chalkboard enshrines the schoolmaster and white surrounds the students. The sentence finishes with lilting synchysis (peach white of the plaster walls). It’s not a first-rate long sentence, but it is one of my own.
While I can provide technical tips on building long sentences (polysyndeton, anaphora, semicolons, parentheticals) technical details alone do not build good long sentences. The long sentence must move in theme and narrative with specific direction and should not meander like an aimless daydream. Perhaps, in this case, it is best to learn through example.
Its vanished trees, the trees that had made way for Gatsby’s house, had once pandered in whispers to the last and greatest of all human dreams; for a transitory enchanted moment man must have held his breath in the presence of this continent, compelled into an aesthetic contemplation he neither understood nor desired, face to face for the last time in history with something commensurate to his capacity for wonder. -F. Scott Fitzgerald, The Great Gatsby
It creeped him out, the way it just sat there looking so plastic and harmless among the old-time good intentions of all that downtown architecture, no more sinister than a chain motel by the freeway, and yet behind its neutral drapes and far away down its fluorescent corridors it was swarming with all this strange alternate cop history and cop politics—cop dynasties, cop heroes and evildoers, saintly cops and psycho cops, cops too stupid to live and cops too smart for their own good—insulated by secret loyalties and codes of silence from the world they’d all be given to control, or, as they liked to put it, protect and serve. -Thomas Pynchon, Inherent Vice
My very photogenic mother died in a freak accident (picnic, lightning) when I was three, and, save for a pocket of warmth in the darkest past, nothing of her subsists within the hollows and dells of memory, over which, if you can still stand my style (I am writing under observation), the sun of my infancy had set: surely, you all know those redolent remnants of day suspended, with the midges, about some hedge in bloom or suddenly entered and traversed by the rambler, at the bottom of a hill, in the summer dusk; a furry warmth, golden midges. -Vladimir Nabokov, Lolita