The trouble with trying to recommend good websites about writing is that the good ones are huge. You can get lost for days in that forest of words. But with any luck, you’ll emerge on the other side as a better writer.
Writer’s Digest – this is for sure one of those huge sites that I just mentioned. Everything you could possibly want advice on is here, as well as writing competitions, workshops and bootcamps. Some articles that I have bookmarked (and therefore found useful) are The 4 Story Structures that Dominate Novels, The Two Pillars of Novel Structure, and The Value of Show, Don’t Tell in Your Writing.
i09 – io9 is more generally about sci-fi and fantasy, but that link right there is to their free advice on writing by Charlie Jane Anders, who’s a Hugo award winner so she knows what she’s talking about (you can read a few of her stories for free on tor.com, and I recommend that you do). Even if you don’t write SFF there’s tons of helpful stuff. There are articles on world-building, writing an ending, characterisation and overcoming writer’s block, which will be invaluable to any writer.
Scribendi – another big site with a ton of advice. As well as info for authors, there’s also articles for students and academic, business writers, and writers of English as a second language.
The Guardian – yes, I know it’s a newspaper. But there’s some great writing advice on there. For example, see Ten Rules for Writing Part One and Part Two, where famous authors give their top ten(ish) tips.
Chuck Wendig – a writer with a great blog. Advice on everything you can think of, and then some. Although this post is about writing advice, you’ll also find great info on there about self-publishing, marketing, and blog writing.
John Scalzi – his blog isn’t always about writing advice, but here are some posts that are: John Scalzi’s Utterly Useless Writing Advice (ha!), Novel Writing and Related Topics FAQ, The Real World Book Deal Descriptions (not really writing advice but interesting to read nonetheless).
Want some more?
My writing advice tumblr – Not my advice, but posts reblogged from around tumblr. Posts that I’ve found interesting or helpful; some that I’ve reblogged to read later. You might find them interesting too.