There's really no easy answer to that. People write in different ways. Some people swear by outlines--personally, I can't stand them, particularly for writing fiction. The key is to find what works best for YOU. So if outlining helps you to organize your thoughts beforehand, go for it. If you feel like outlining cramps your style and you'd rather just go with the flow, then do that. Outside of school, there really isn't any one correct way to write. The most important thing is to be able to silence your inner editor--that little voice in your head that critiques every sentence you write and every idea you have, and makes you so afraid that what you write won't be good enough that you don't write at all. It can be really hard to do, but you have to ignore that voice and just write. Yeah, what you write may very well be crap. So what? I promise you every good writer produced MOUNTAINS of crap before they became good--because practice is the only way to get better. And if you DO write something that's absolutely terrible, you don't have to show it to anyone else. You can toss it in a fire somewhere and say "Oh well, at least now I know what NOT to do." Then the next thing you write can be better for it. And once you start putting pen to paper and actually writing, I promise there will be moments in which you'll surprise yourself by coming up with a sentence or a turn of phrase that's REALLY good. It's a great feeling. Sorry for rambling, but hopefully I've helped. =P You should check out NaNoWriMo (National Novel Writing Month). It's great in helping give you the motivation to actually sit down and write.

https://www.reddit.com/r/scifiwriting/comments/3nm3b7/ive_never_written_anything_before_and_i_want_to/