1) Just because you think your writing is terrible, that doesn't mean it isn't. True enough, so often we as writers begin to assume that our judgment has become clouded and we begin to fall in love with our own work despite all obvious indications that it needs deep revision. This is why candid input from a professional editor can sting so. We've convinced ourselves that bad is good, and therefore good advice must be bad advice. My advice: accept that your first draft will be bad. It will be terrible. Embrace that fact and look forward to the revision process!
2) Moving backward is the opposite of moving forward. I would accept this as an axiom, but so often we pause when writing and scroll back up the page to re-read what we have written. Bad call. The time for re-reading is after the first draft is done. Keep moving forward. Never look back. Even if you know for damn certain you've made an error, remember there will be a time for revision later. Now is not that time. Keep writing. Keep moving that word count. Going back to do spot-edits is a slippery slope that leads to a standstill. It's a black hole. Maintain escape velocity and keep drafting until you type " The End."
3) You will never find time to write. Instead, you must make time to write. Hoping to fit your writing project into your free time is a fool's bet. There will always be something more important, more interesting, more enjoyable than getting the writing done. Instead of fitting it in, carve it out. Make the time to write. Never let mood dictate whether you can produce. The best case scenario is to choose a manageable chunk of time, the same time every day, and reprogram yourself to simply sit and write. At first it will feel like a chore, but just as you get over the "muscle soreness" of this new exercise, you will find that mood has less and less grip on your ability to write.
4) If you make it too easy on your characters, you make it too easy for the reader to stop reading. Be sure your character has to work for his or her goal. Well, let's back up for a second. Be sure your character has a goal. A very specific, achievable goal. Then place very specific obstacles in your character's path. If the path to the goal is too easy, it won't be interesting to read. Up the stakes. Make them dire. For every individual scene identify what there is to gain if the character succeeds, and what there is to lose if he fails. And always ask "is this too easy?"
5) Writing is about storytelling. Never lose sight of this. You may very well craft elegant prose, playing with layers of meaning and timbre of dialogue. But the most artful and nuanced writing must serve a purpose. You're leading a reader through a story, not simply describing a sunset or detailing a character's day. No matter how interesting a character or snappy a dialogue, be sure there is a point to it. A conflict. A rising action. A resolution. Your prose must justify its existence, and in doing so you justify your existence to the reader. That's your job, after all.
6) Love what you do. It's so intangible, so difficult to prescribe that it barely counts as advice. But a reader can tell when you love your story, your characters, your settings. Enthusiasm oozes through the words, between the lines, beneath the dialogue and above the subtext. Love is palpable, if not quantifiable. If you hate your story, then for the love of all that is holy, stop writing it. Find the story you love to tell, then tell it. I won't say that all you need is love, because that's patently false. But without the love, you run the risk of writing "boring." And "boring" is death.