[US_TOML]

You were probably expecting some more no-good rules from me, right? :D
Not today.

What should I do to prepare to write a story?
Should I develop my characters and KNOW them inside and out?
Their friends, family, hobbies, where they live, eat, etC???

[Sticktator]

If it's a dynamic character, then yes, certainly.

If you don't beforehand, then it's definitely going to end up with more editing at the end, which may spoil the magic a bit.

[Expendable]

A concept. Where do you want this story to go?

Then some characters.

A setting, something appropriate. (Or maybe not....!)

Find some good reference material (if you need it).

Maybe an outline to keep you on track. Some like the Snowflake method (http://www.advancedfictionwriting.com/art/snowflake.php).

Then write.

[Ranke Lidyek]

There are many approaches. The main thing is to show, don't tell. There are writers who function best on the fly and there are those who need to obsessively outline. My recommendation is to just start writing. Write from the heart until the story ends. Then edit with the head.

[MrBF1V3]

Yeah, it kind of depends how your brain works, or in my case if. If you're not sure, try everything, keep what works.

I usually start with a good sentence, and write a scene. If I can get four or five good scenes I start editing them together and make it into something that works.

B5