Planning is crucial, what I've learnt...

Most of the time hardest part of writing, for me, is finding the inspiration to start and complete a story.
Often times I get great story starts and can write chapters of stories and then all of a sudden I will run out of steam and the ideas dry up and despite trying to concentrate on and focus all of my attention on a specific thought stream I end up with multiple idea's for different stories running around in my brain but no extra ideas for the already established story.

I have learnt to combat this horrible condition of multiple story syndrome, with planning!
Honestly as a teenager it was not something that even crossed my mind, I would leave everything to the last moment. Important written assignment due tomorrow, write it tonight!

Not any more, planning is now crucial. I cannot plan my day at work and how well or poor it will be, I can plan out my stories, give myself an idea of characters and plot twists and when I want to implement them... The story is still written organically, everything developing in its own time. but instead of getting all of these wonderful ideas and cramming them into a few or even 20 chapters and then running out of steam I know now that to spread them out and wrap them up properly is a much better more productive and enjoyable use of them.

The reader enjoys the read, and I enjoy writing them much more.
I keep a folder for each story, often a binder or expansion file, which will contain the character notes, scenes, accessories, and plot maps/notes. I will sometimes brainstorm ideas onto a piece of paper and include that if things don't meld as well as I would like them too.

But the most important thing I have learnt is that you don't always start a story at the beginning... you can start wherever you need to, the end, the middle it honestly doesn't matter. It's your story to tell, however that story evolves for you is how it is meant to be written by you.
Start in the middle and write how you got there, and then where you went from there. It is up to you!