A recent FB thread inspired me to remark upon usage of non-words, as I regularly mock people who use them improperly. I thought perhaps by logging The Rules, we’d be able to curb offenses. So, in our efforts to share with conversational partners that they are, indeed, hilarious, I’ve composed a little how-to of digital expressions of laughter. 

I heard that. You just asked how I came to know The Rules of Digital Laughter. It’s quite simple. This is how I do it. And thus, everyone should. 
The LOL: The primary form of digital laughter comes as the LOL. This means I just laughed out loud. (Technically, our little diddy is inaccurate: it’s aloud. Using non-words as shorthand for a grammatically incorrect phrase just heightens the absurdity). 
Proper function of the LOL: informing your conversational partner that you just laughed out loud aloud. 
Common improper use: a filler, like you would verbally with “uh” or “and” or “mmm”. It indicates that the phrase was heard or the last message was received, but with improper use it lacks the significance of how funny the other person actually was. Speaking as a hilarious person, I’m on a mission to abolish this practice of the filler LOL. To coach on improper use, I tell people, “Literal LOL” to signify that I literally* laughed aloud.  Over time you can remove the use of literal as they understand your mastery of the English non-language.
And why should the filler LOL be eliminated? Because who wants a text that only says, “LOL”? It’s like the Gratuitous Thank You of the business world. An email, empty, except a thoughtless “thank you” serving to tell me that you’ve acknowledged the existence of my action or previous email. Ridiculous. The Gratuitous Thank You is another drain on society.
So, how does one communicate enjoyment of a comment without putting it on the status of the LOL? A few suggestions:
Haha. Quick and simple. It means “I caught that joke”
HA! The blurt approach. Much like a Bah! but quicker. It might be translated as “Please hand me a towel to wipe the coffee from my monitor.”
Hehehe. A polite chuckle of the non-literal variety. 
Depending on your laugher style, there could be further options. Are you a cackeler? Or whooper? Then perhaps you can translate that into your digital laughter response. Let us hear your voice. My cousin Kimmy should drop LOL altogether for “aaaaaahhhhahahahaha hahahaha ahahah.” She would type that in a red font, as red always translates well into high-pitched squeals. 
ROFL and LMAO/LMBO/LMAO? These are just silly. No one above the age of 17 should use them. We’re adults. We don’t need code. No one will tell your mommy if you found the joke funny. And besides, the un-literal use goes beyond the LOL. Rarely do I see an ROFL remarking on something of true hilarity. 
*This would lead to a lesson on the proper use of the word literal. This means actually, in real life, not an exaggeration. You do not literally “see red”. Rule #1, never use the word “literal” with metaphor or simile.