Art is subjective, purely subjective. The breadth of human experience is vast and although there are universal elements, there is simply no way to define a scientific formula for a successful story.
Some are brilliant because of their subtley of theme. Some are heart racers, fast paced blurs of adventure, better than an aerobic workout. Some are slow and intellectual, building a logical progression of plot, character and theme with solid blocks of narrative.
But I must say that the most sure fire way to engage a reader is to drag them into your story, kicking and screaming, leaving them breathlessly wondering 'what next'. Once you've got them hooked, go subtle. Once their minds are engaged, go intellectual.
Particularly, I've noticed, with the short story format, and even moreso with work designed for onscreen reading.
The eBook market is growing daily. With Kindle, Kobo, Sony, Nook and now the new iPad, your digital book or story is going to have to compete against more than just other books. Most digital novels are read on computers still. Your work is going to have to compete with an endless array of internet distractions; distractions that are interactive, proactive, and brightly colored. If you're publishing prose and poetry online, or seeking to have it published, you're going to have to compete with applications and social networking and news sites that are IMMEDIATELY emotionally satisfiying and provide connection. You need to grab them by the heart or the head or the hair in the first scene. Or they'll get bored and go check their facebook friends. So much for the preview of your new digital novel.
Start with a bang. Start with action. Start with a crisis. Start with the stakes already high and make them the reader's stakes as well.
You may not snag every single reader on earth, but you know what snags you and however unique you may feel you are, there are a couple million other people out there that have the same buttons.
If you want to slow down after the first scene or three, give some backstory, lay down some beautifully worded tone and setting, then is the time.
Whether you're writing finely tuned literary fiction, fantasy, philosophical musings on society, humor or erotica, to keep the attention of a digital reader, start with your turbo engines engaged.