10 things every writer should know before they start writing.
1) Basic plot. You need a beginning, a middle and an end. And basically, that is all you need to have. You can fill in the gaps later. Right now, there are more important things than plot to worry about.
2) Characters. I don't mean knowing the names, ages and what they look like. You gotta know how old your female MC was when she got her period, or how old your male MC was when he got his first stiffy. You need to know their grandmother's mother's maiden name. You gotta know how often they have sex. You gotta know if their mother has a skin condition of unknown origin, and if she does... exactly why is the origin of that skin condition unknown? These aren't just dolls! They are fucking people. If you're gonna pen down their story, you better know them better than their mothers do.
3) Genre. I know, I know. But you don't want to start a story as a romance, venture into erotica, then become a suspense/thriller, then sci-fi before finally settling into horror... just before it turns into a western, complete with "Well howdy there partner." Know what you're writing, please.
4) Setting. A story has to have a place to happen. Sure, the characters can travel, if need be, but they need a definite, central place for the story to focus on. Having fifty different places in one story makes for hectic reading.
5) Timeline. Some stories span hours, some days, some months and some even span lifetimes. You got to know how long this shit is gonna take so you can write accordingly.
6) Conflict. Gotta know who or what your characters are up against. There must be conflict, be it internal or external. Know the conflict. Make it fucking impossible to overcome. Then... have your characters overcome it anyway. "Protags must protag... and antags must antag." (Cathyfreeze said that on Absolute Write Water Cooler forums oh so long ago.)
7) Who is gonna win. Bad guy? Good guy? You decide, but you had better make sure that decision means something and isn't just because that is how you want it. No: it doesn't matter if it makes no sense in the story if all the other people die, I just want this one little girl to live, alone in the world with nothing but chain grocery store leavings to feed her for as long as her lonely lifespan lasts, which if I had my way would be forever and ever and ever and... shut up. Make your decisions count. Don't just do some stupid shit cause you want to. The story isn't really yours. You may create it, but it isn't your story. It is the story of the characters. Make sure it stays that way.
8) Will the winner of said conflict come away basically the same? If so... stop. Rethink. This is not so the character just goes on about his merry way like he or she never even went to Duggard Academy and got ass-raped by a baboon. It doesn't work that way. This shit changes people when it happens to them in real life and so, it must change your characters. They are, after all, people too.
9) How will this conflict change the world for your characters? This is not the change within the characters themselves, as is listed in #8 of this post. This is how things around them change. Do others feel the change this subtle conflict resolution has brought? If not, why not? If so... how... and why?
10) This is the absolute most important thing any writer should know before they start. Writing is fun. Writing is therapeutic. Writing is a great way to kill off a certain someone time and time again... all while being perfectly legal for you to do so because it is fiction and has no affect on the person in reality. They needn't even know you've killed them (or how often). If you aren't having fun, you aren't doing it right.