There are two ways to go about a painting in my book. by planning, and simply by painting. Either way the first things i do every time is pick a few colors and let them mix to create a background
With this painting i had the luxury of a vague idea in what i wanted to accomplish so once i had the background down i went ahead and just blocked out the basic shape. After that it was just a matter of hashing out the image.
I find that its very important to be loose when painting in the beginning, done get hung up on small details or imperfections, especially if you are working with oils. If you made a mistake, odds are, you can fix it later just as well as you could now, (sometimes better as dryer oils tend to spread less). Just keep working on sharpening the image. layer by layer, use only as much paint as necessary if you don't want to muddle things .
Stick at it and before long you'll be able to refine images whilst attacking your canvas with brushstrokes like the late great bob ross.