You really should read the answers, Monica. As I have commented, many of them say the same things.
Make writing a habit
Amadeus: "Basically [Stephen King] said, if you want to write, write. Every day."
Chris Sunami: "Be in it for the Long Haul: Writing, especially as a career, is an endurance race, not a sprint."
Cloudchaser: "Write as if it was your job"
SR. Prairie Wind: "... always keep a journal ..."
Enjoy writing
Amadeus: "That most people that claim they want to be writer are fooling themselves, because what they want is To Have Written. ... but they don't actually love writing for its own sake."
Chris Sunami: "Make Peace With Writing For Yourself ..."
Galastel: "Write what you love writing, enjoy the process, do it for the art - not for the money."
Cloudchaser: "Enjoy writing"
Don't aim for fame and fortune
Amadeus: "'They want this,' [Stephen King] says, waving at the set and his interviewer. The interviews on TV, the book signings, the money from a best-seller ..."
Cloudchaser: "Be content with making a living"
SR. Prairie Wind: "Most important, for those of us that may never see our thoughts lithographed in production."
Write the next book
Chris Sunami: "One book is not a career: ... you'll need to keep on writing and publishing."
Cloudchaser: "Write the next book"
GGx: "... don't hold onto your writing gems because you think they're gold dust ... When I wrote my first novel I thought, I'll never come up with another idea this good, this has to be the best idea I'll ever get. I held onto it and honed it and honed it until I'd flogged the damn thing to death. Then I wrote my second novel and thought, no, no THIS is the best idea I've ever had. This is it, if I can't sell this, I can't sell ANYTHING. This is the end of the idea road, it doesn't get any better. And then I came up with my idea for my third novel!! :)"
Consider the reader
Read
There is some additional advice in the second answers from Amadeus (which limits itself to fiction and does not take the general perspective from which I asked the question, so it could be deleted) and SR. Prairie Wind as well as in the answer by Chris Sunami, but basically that's the summary of all the answers.
As you can hopefully see, the answers aren't as varied as everyone, who thinks the question is opinionated, claims. And if you delete all the one-sentence answers by low-rep users, points 5 and 6 are gone and the four pieces of fundamental advice, that I was aiming for, clearly emerge.
For the moment I have protected the question, because all the recent one-sentence-answers were by new low rep users.