This is going to be short, because I'm new to it, so no point in torturing anyone longer than I have to and tired (since I've just finished building this website).
The struggle with many things for me is just starting... Very often once I start its fine, the pieces fall into place, the road maps itself out and you know where and how you're going. Even if things go a bit awry, you have momentum and some foundation to work from.
Sometimes though, I just spin my wheels...so many things to do and each one seems important and it seems like a symphonic orchestra warming up in my head...So I make lists; real 'old school' I know, but it helps me narrow down what needs to be done first. Then its about starting it.
When I'm nervous about starting a new painting, or haven't painted in a week or so because of life intervening, then I may just "warm up" with working on my paint charts, or working on a drawing, preparing panels, or just a little studio housekeeping. Then I lay out the palette, get my brushes and start, remembering what Juan Martinez, (a great instructor at the Academy of Realist Art) told me in a workshop, 'you can't tell if its wrong or right until you get it on the canvas.' Once I've made that first mark, I'm always shocked at the time that passes before you've realized you've made hundreds of marks and a painting is somewhere along its path of creation.