Everyone sucks at first when they start writing. Everyone sucks, but they suck in predictable ways. There are really only two ways to suck at writing, or pretty much anything creative. One way involves knowing you suck at this new endeavor, and knowing a little more every time you go back to your work. This way brings discouragement and abandoned projects.
The other way to suck lacks self-knowledge of how bad you are at this new mission. Those who suck without knowing it may be discouraged by a society that fails to appreciate their greatness, but they never consider whether greatness may be lacking in themselves. These are the ample producers of junk.
There are two ways to suck at writing, or pretty much anything creative--but there's only a single way to not suck.
The only way to not suck is know how terrible your work is, but to nevertheless stave off the despair that follows on the heels of that realization. The only way to not suck is to re-write that piece so that maybe it sucks a little bit less, and then write another piece. Maybe that next piece will start off a little better than your last attempt--but you revise and improve it anyway, because it still isn't good enough.
The only way to not suck at writing, or pretty much anything else, is to come back to your work again and again. Step by painful step, eventually your work won't suck--at least not all the time.
The internet bubbles over with bad writing, and all sorts of other kinds of bad art. I don't mean bad in the sense that I don't "get" it; I mean bad in the sense that the conception and execution leave no "it" there to get. That's okay; we all have to suck at first. I've filled my corners of the internet with enough terrible work that I shan't cast the first stone. I just look forward to seeing what becomes of the few who realize they suck--and then don't give up.