1) Write what you would want to read.
First, ask yourself this question. "Would I want to read this?" I know this sounds simplistic, but if you aren't writing about a subject that you care passionately about, there's a good chance that your reader will recognize that fact and not be very interested in reading it either.
2) Write with clarity.
If you aren't familiar with a certain location, culture, time period, etc. that you intend to write about, then do research on it first and write it later.
With that new-found knowledge at-hand, your writing will translate to your reader with more clarity.
3) Write, write and then write some more.
From my experience in working with many writers, what appears to be the biggest impediment for them is they just can't seem to find the time to finish what they have started.
Even, if it's only for one hour every day, find the time to write and then do so! The more you write, the better you will be at it and the more work you'll actually complete.
Any craftsman/craftswoman improves with the act of doing what it is they want to do best. And, so too will you in the craft of writing - simply by following these three simple steps to writing, more.