The standard advice about turning paper prose into screen prose is to make it shorter and more "scanable," because screens flicker, tiring our eyes and brains, and so we scan for what we need and jump to some other resource if our needs aren't instantly met. Now that more than 50% of digital consumers consume via cell phone, the desire for brevity is even greater.
In truth, all transactional prose should be task-oriented and reader-efficient. So the advice above transcends the medium. It is also based on the assumption that writers today "turn paper prose into digital prose," whereas in fact nearly all prose is now born digital. It's just not always well adapted to its medium because the people who teach writing, for the most part, didn't learn to read or write digitally and so tend to offer advice that smells of ink and paper and paste. Ten years may see the end of that, but cultural lag will slow the digital transformation: education is inherently conservative. It is, however, also true that what a digital writer needs to learn is very different from what our predecessors had to learn.
Content creation and distribution -- aka writing online -- is a broad skill set. You need to know how to do the things listed above or work well with (for) those who do. Learn some programming fundamentals. Our world is digital; you need to transcend the analogue (paper-based) ways of thinking and writing you've been schooled in up till now.
Among people who like to complain, complaining that digital media made txt spk rool is a common topic. New conventions always annoy some people. Text speak, by the way, was created back when 9-character key pads meant a single letter might require 3 key strokes. The inevitable stroke economy led to truncated expressions, to say nothing of crazy typos that prefigured the genre of auto correct fails (NSFW). Since cell phone key boards now have all characters, using txt speak is just a counter-productive way to signify your digital hipness. Or save a few nano seconds.
Txt was also used for encryption by teenagers trying to avoid parental supervision: mos, ffs. By now, of course, many of those kids are parents themselves. Generally speaking, txt is conventional when literally texting but counter-conventional everywhere else. Say lol out loud next time you need someone to like omg roll their eyes. Nothing suggests haste and carelessness like txt in an email.
The tools we use influence the messages we send, often in ways we don't immediately notice.
The emoji is a transformative digital writing artifact, making pictographs central to alphabetic script. Most people just use emoji as some variation on an exclamation point, but some digital writers can string whole thoughts together and if I'm not mistaken, someone has written a whole short story using them (I should Google that, of course, rather than using the very old fashioned dodge of "as I recall.") For you recent history buffs, here's an article about the origin of digital poop.
One of digital writing's most common features is caused by how digital writing gets paid. Because data analytics count eyeballs per screen, getting people to click has become a primary goal for people writing link lines. Thus most headlines are now some version of a riddle, where the most important element of the story is left out, to entice you to learn more, by clicking, or to see if you guessed right, by clicking, or to see if your favorite is among the top 10 whatevers, by clicking. Click bait.
Another rhetorical phenomenon caused by digital affordances is the prevalence of lists. Because people like to read short forms when reading online, lists are enticing. Which article lead would you rather click on: Solar Energy and the Future or 5 Things to know about Solar Energy. The later is much more inviting because it suggests a quick read, sorted for easy screen consumption. The former sounds long and complicated. On the other hand, anytime you see a 5-things-to-know headline, you might think click bait slide show.
And the effects may outlive the cause.
The death of cursive (hand-writing) is a parallel complaint about how the digital ruins everything good and wholesome. Once we no longer teach cursive, a whole generation will not only lose the ability to write cursive script but also the ability to read cursive script, so what will become of the written documents upon which our world depends? How will the young people of today read The Constitution? I'm harrumphing the harrumphers here because the most important manuscripts are digital now, and are available in typescript translations. But there's no doubt that the digital has brought big changes and more even greater ones are on the way. If digital assistants like Siri and Alexi and Ask Google win, the keyboard will be obsolete, and the spoken may replace the written, just as the written once replaced to spoken as the primary medium of business correspondence.
The greatest change wrought by digital writing is the erasure of the line between public and private. Everything we do today that involves the internet, from buying products to consuming services to meeting people, is logged and tracked, sorted, analyzed, bought and sold. Most of your data trail is anonymous, but it can be de-anonymized easily enough. We seem to have embraced this fact, some of us at least. We are willing to say and do things now in public spaces that our predecessors would cringe to think about let alone do. The illusion of anonymity and the bogus courage of distance plays a part here. But I think that because we can no longer disengage without entirely giving up our phone, most of us are simply indifferent to our loss of privacy. In fact, I think many of us "private citizens" seek publicity, via Instagram and Pinterest and FaceBook, even though we know it makes us big bright targets for advertisers and politicians. In the 1980's there was a joke, told in a "Russian" accent: In America you watch TV; in Soviet Union TV watches you. That's no longer a joke. All of our devices are always watching us.
For all of pre-history, presumably, and historically for sure, change happened slowly, generation to generation or slower, unless some natural phenomenon like drought or volcanic eruption forced our ancestors to run. The industrial revolution accelerated human existence and now generational changes happen every five years. The world I was born into didn't resemble the world we live in and our world won't resemble the one your children inherit.
You were born digital, but you weren't taught digital, not fully, and you need to pick up your pace because what is cutting edge today will be obsolete five years from now.
You need to learn how to teach yourself. What you learn is, of course, up to you. But I think you should consider extending your computer skills to include coding. W3schools.com is the best free resource I know for getting started.