Is it some silver pencil clutched in a future writer's newborn hand? Some sort of chemical reaction to over-absorption of ink from a thousand paperbacks, since recess was still a facet of daily life? A religious adherence to proper grammar and a study of story structure?
Depends. What is defined by "good" writing?
That comes down to knowing your audience, and finding a way to reach them.
Easier said, than done. Right?
Which is why it is usually best to write for YOU, and you will find your audience. And by "find", I mean you will slave to discover them one at a time. At some point, you may strike lightning and have the masses flock to your piece, but that is no guarantee, and all you can count on (if you have done "good" work) is to grow that interest one grain at a time.
Now, as to how to make that work "good", so that it is liked by anyone else? That's an even harder question. Who likes Twilight? You may frown and spit, but the series has millions of rabid fans. This is an old argument, but look at Harry Potter, again: HUGE! But there are those that burn the books as if they were a sign of the devil.
Point me to any popular book and I'll point you to a base of anti-fans that make the zombie-apocalypse look tame.
Point is: what is "good", is subjective. You only have you to consult with on a regular basis, so make it as good as you can. Make it so YOU like it. Don't fret to revise it, rip it apart, burn it and rewrite from the ashes. Then share it and take feedback. But that feedback must filter through you and what you want to achieve. You may find wisdom in it to sip, perhaps gulp, or it may just be a bitter swig to pour down the drain.
Just make sure to thank them for the cup, no matter the end result.
So, in the end, it could be simply answered...
What makes a good writer is to be true to yourself (your voice, your story), to revise, and to persevere.
Unfortunately, what makes for good writing, is entirely subjective.
A kick in the laptop, I know. But hey, that's life. Turn your cheek and keep on.
Know that you will be a good writer, long before anyone really considers your work to be good writing. But for the fanatical among us, we will blindly stride forward, even if we trip, fall and bounce off the rocks.
Happy Writing! And thanks for reading this motivational beat-down.