As far as possible, avoid thinking about writing. Do your thinking while writing.
In this post, "Thinking about writing is different from writing", I said:
Over time, I've found that I can solve any writing challenge -- when I'm writing. As much as possible, I avoid thinking about current projects too much when I'm not in front of the computer, or when I don't have a pen in my hand.
Get your thoughts about your project onto the page. Write about your writing when you're confused or uncertain.
For example, if you're writing a novel:
I'm not sure what I need here. Benny Cleaver [the protagonist in your short story] isn't coming to life. There's no logical reason for him to take the attitude he does. What if something happened to him when he was a child, and he's completely blocked it out?
Or you're writing a Web sales page:
I'm not sure what I should emphasize here. The client's competitors all seem to be using the sales material from the manufacturer. I should start by checking parenting forums, so that I can see what people are saying about the product. Maybe interview a couple of real life customers?
When you write about your project as you're developing the project, not only are you writing (your best ideas will always come when you're writing), you're also documenting the project. Days, weeks, and even years later, you'll be able to see what your thinking was, which means you can drop a project and go back to it.
Most importantly of all, you'll find that when you document your projects in this way, you'll build your enthusiasm, so that you're eager to start writing each day.
Want to make your writing easy and fun? Discover my Top 70 Writing Tips.