I find it impersonal to tell someone to "just write" or "write well." People will tell you to "write this way," but seldom say it with a welcoming "right this way." Instead of creating an easier-said-than-done situation, I'm just going to tell you some of the ways you can pick up writing without great expectations.
1. Write what you know.
Anyone that's survived their childhood has plenty of material to share. Experience is priceless and only you know how to show and tell us. Write what we don't know and even if we do know, you know the same thing but differently too. Your thoughts on the matter are what matters and writing will help you know more.
Chances are what you enjoy reading will become what you enjoy writing. The subject matter and genres speak to you and your voice has more to add to those conversations. Love what you do and do what you love.
The human vessel holds precious cargo filled with emotions. Let it out of you and make sure it lands on the page, all of it. We can assess the damage after a full report. Asserting those fervent feelings can only heal you, not harm you.
4. Write for you.
No one knows you better than yourself and you can't please everybody. The people of Earth are insatiable purveyors and surveyors of entertainment and adventure and fantasy and everything in between. Write what you like because you are your truest fan.
5. Write what you care about.
Those that love you and support you are going to make it into your dedication page. Even if it's one person in the crowd, it's still worth doing. Write for who you care about and those who care.
6. The pen is mightier than the sword.
Remember the saying, "Sticks and stones may break my bones, but words will never hurt me?" Words can affect us. We remember what someone said, where we were, where we are now, and where we are going because of it.
7. Speak your voice.
There's many unique styles of the written voice. William Faulkner is notorious for having the most difficult to dissect for lack of pause with punctuation. J.R.R. Tolkien takes time with his descriptions, sometimes worth an entire chapter in itself. Make sure that your story is told by you, not your mentors.
8. Your stories are unique.
The ideas you have are yours. Don't let anyone take that away from you. Only you can tell it best. The rest is for readers to interpret and for writers to aspire to.
9. Be wary of adverbs.
Really, very, happily are fine words, but can come off as lazy. Don't get me wrong, there's a time and place to use them but they should only be used when necessary or appropriate. Expand your vocabulary instead.
10. Do not clutter.
This is a side note for vocabulary words. Avoid using them consistently. You can provide context and clarification for these words but it's more fun to have your readers wonder what it could mean and discover its importance. That's the fun of writing and reading!
11. Tell the truth.
Everything you learned, were taught, and know now and will eventually know has to lead you to this moment. Your experience has to come from you. You can bend the facts but only once the facts are established. Wouldn't want a lawsuit on your hands from that nosy neighbor or girl that dumped you because she convinced you that "it's not you, it's me." Now, the truth, the whole truth and nothing but the truth good sirs and madams.
12. Start now.
Procrastinating is not a substitute for thinking nor is there a substitute for hard work. Preoccupy your time with hobbies or tasks that don't have you thinking all the time. The mind is a muscle, so don't strain it, train it. Mixing things up can be enlightening to your process as a writer. As long as what you're doing can make you think and feel a little differently from what you had intentions for that wouldn't make it to the surface quite yet. Yet! There's a word. It will happen, but it doesn't happen if you don't start now.
Writers don't magically summon inspiration after eating a bowl of alphabet soup. It takes time to express who you are on the page. Keep writing and you'll never go wrong.