Contrary to all those times you've heard a writer confess at a reading that he writes fiction because he is a pathological liar, fiction writing is all about telling the truth.
Don't confine truth to fact. Imaginative truth is as powerful, and often enough, more so than fact.
Don't write your books for people who won't like them. Give yourself wholly to the kind of book you want to write, and don't try to please readers who like something different.
The fictional world seems larger, seems to have more dimension and richness when, for example, the protagonist from one novel you've read has a cameo role in another. I think that recognition is a very, very powerful phenomenon; it is one of the deepest and greatest pleasures of reading.
If you want to be a writer, you write. Everybody wants to get published. You gotta play your long game.
The silver lining of those years when I was trying to get 'Tinkers' published but couldn't were the years when I had to decide, Why do I want to be a writer? I realized that writing is the thing itself; writing is not a means to publication, writing is not a predicate of publication, so I spent years making art for art's sake.
I'm no online whiz, but I'm not a Luddite, either. I love that we have these laptops and tablets and smart phones; they're awesome and convenient and all that. It's more about maintaining balance. Technology should always be a predicate of the true subject: our individual humanity, our examined lives.
I worry that if whatever pops into your head at any instant immediately goes online, you lose the crucial time for your thoughts to simmer and evolve and build up nuance, depth and empathy.
Write as precisely and as lucidly and as richly as you can about what you find truly mysterious and irreducible about human experience, and not obscurely about what will prove to be received opinion or cliche once the reader figures out your stylistic conceit. There's all the difference in the world between mystery and mystification.