And you learn to write by writing, just as you would learn to play the piano by practicing a lot. Most people don’t like hearing this, but writing is work, and it takes skill and practice, just like any other art. Also, no job is 100% fun, and writing is no exception. Every writer has things they don’t enjoy writing; for me, it’s transitions and “council scenes;” for one of my good friends, it’s action; for another, it’s detail and description. But it’s practically impossible to write a really good interesting novel that’s nothing but dialog, or nothing but action, or that doesn’t have any transitions or descriptions. You have to make yourself do the parts that aren’t fun, and do them as well as you can, because no one else is going to do them for you.
Second, get really good at the boring technical bits: learn how to type, to spell, to write a grammatical sentence in your sleep. This is terribly important, though a surprising number of people seem to think they can ignore it. Also, remember that if you are going to be a writer, you are going to be a self-employed businessperson. Learn about things like keeping good records and watching your finances and figuring out financial statements. I’ve saved myself several thousand dollars over the years because I checked the math on my royalty statements and did some simple comparisons with previous statements.
Third, read a lot — and not just the kind of thing you love and want to write, but a little of everything. As a reader, you can love fantasy or science fiction and not want to write anything else, but as a writer, you need to know what else is out there and how it works… and reading, say, Westerns or mysteries or historical fiction may very well give you ideas for things you can do in your fantasy or science fiction — ideas you wouldn’t have gotten elsewhere.
Finally, have a life. It is hard to make anything in a book sound interesting if you aren’t really interested in anything in real life. It doesn’t matter what you decide to do, as long as you try a few different things and find something that you really enjoy. It could be cooking, or being in the school band, or scuba diving, or building your own computer, or gardening. Or cats. The more you do, the more you will have to bring to your fiction. (This is one of the reasons so many writers’ biographies have such an odd list of things they did before becoming writers: “He worked in a biological research lab for a year, and then he spent two years at sea as crew on an oil tanker, and then he worked in Alaska taking photos for a travel magazine, and then he became an insurance adjuster, before turning to writing….”)
Oh, and keep in mind that there is no one way to go about writing something. There are as many different ways of writing as there are writers; one of my dear friends outlines everything, another just starts with a blank page. I know authors who start at the end of a book and work backwards, or the middle and work outwards on either side, or who jump around from Chapter 4 to Chapter 10 to Chapter 7-8 and so on. It doesn’t matter what method you use to get the words onto the page; what matters is that they are all there, in the right places, by the time you are finished.
Some writers, though, can’t show their work to other people until it’s finished without spoiling it or losing the desire to write. Those people, obviously, should not be in a critique group, because it will just be frustrating.