Hrrm. Trying to boil it down to what would be most useful to someone only just starting is not easy.
I think the first thing, would be; find a working habit that reliably generates the actual words. Some people strongly advocate writing every day; if that works for you, fine, but you can still be a real writer if it doesn't. (Extreme example for a real and successful genre writer's habits is that I've heard Iain Banks say that his process is to write a novel in six weeks of panic and spend the rest of the year goofing off.) My own practise is to write one night a week, usually Friday, and catch up in advance if I am going to be away, and that has been pretty reliable in terms of generating a novel's worth of words a year.
Second; it's going to take a while. There's a lot to learn, and it takes a lot of actual writing to learn it. The chances of any individual new writer both being a once-in-a-generation brilliant genius from the get go and being recognised as such and picked up from the start are negligible; but becoming a better writer than you are is possible and worth doing.
Third; good beta-readers are more valuable than plutonium dust. Good readers should ideally; understand and sympathise with what you are trying to achieve; be entirely willing to tell you what sucks about your work, no matter how hard it was to achieve it, and equally be able to see and reinforce what's good in it; and absolutely ideally, should be moderately better writers than you are. (Writers less good than you aren't helpful sources of advice for obvious reasons; writers much better than you are likely to have points to make you basically won't really get, until you have got closer to their level.) It helps to learn not to take "this book is not doing a thing i am interested in" as "this book sucks", too.
Fourth, be familiar with your genre. If you're writing a book set on Mars, get some handle on what the classic Mars novels are - because whether you want to be like them or not, people are going to compare your work to them.
Fifth, don't only read genre. The failure mode of doing that is writing books that read as bad rip-offs of bad rip-offs of bad rip-offs of Tolkien. besides, the more widely you read, the more cool stuff you find that you can use. (As William Goldman says, everything is research; you just have to figure out what it's research for.)
Oh, and number six; it's perfectly fine to start with exercises in learning how to do a certain thing. To write stories where you're trying to get a plot to hold together and will worry about making the characters emotionally real later, and so on. Keep track of what you're trying to learn when you're writing something. It's also perfectly fine to have a great story idea and realise you're not up to it yet, and work on something else first.
