There doesn’t need to be a plan. Most of the time I write a few chapters before I have any idea where the story is going. Once I know I jot down all my ideas and plot them into the order they will appear in the story (otherwise I get completely lost!).
If I have a clear picture in my head for a scene I always write it down as soon as possible (there’s nothing worse than promising yourself you will remember only to forget everything completely the moment you have a pen in your hand). I’ll jump ahead if a scene forms that’s further ahead in the story, keeping it somewhere I can easily find it when I get to that point, otherwise I try to write in chronological order. The skipping ahead parts can be the best parts of the story if you catch them while they’re clear in your mind.
I have had to drill myself into continuing to write even when the writing is terrible. It doesn’t matter if it’s god awful. It can be edited later. Over and over, for as many times as it takes to get it right. The end product never looks anything like the original idea, you’re better off embracing that notation from the beginning and going where the writing takes you.
Write now, edit later.
Two years ago I had an idea for a story. An idea that has lingered in the back of my mind every day since it first arrived; building characters and a plot, the picture growing clearer. I regret that it has taken me until now to really take the idea from my head onto paper.
Don’t have regrets. Just write it. What’s the worst that could happen? (Quick write that thought you just had down to torture a character with later!)
You don’t need a perfect time, a brilliant plan, you just need to start.