When you're beginning a painting from a subject, the same principles apply, whether it's a still life, landscape, or portrait, and whether it's realist, impressionist, expressionist, abstracted, or some other style. You can only take one step at a time – and you can't get to the end before you've begun.
Generally, new painters want to skip the preliminary steps and go straight to painting luscious detail. But – you can trust me on this – if you skip the preliminary steps, you will go far awry. Then you'll get depressed and frustrated and want to chuck the whole thing - pain that you can save yourself by just taking things one step at a time.
In this demonstration, Gregg Kreutz "Market Flowers" DVD from Liliedahl Video, on YouTube, artist Gregg Kreutz begins by catching the essential gesture of his still life subject. This also establishes the placement of the subject in his composition.
Next, he begins blocking in the large shapes (he has toned the canvas beforehand).
Then he turns his attention to the background. Notice as you watch the video that he does not paint with black – he mixes his darks, creating a much more interesting color.
Only then, once he has established the basic shapes of the composition, does he begin to break the painting down into smaller shapes and greater detail. Here is the final painting, as he puts down the last brush stroke. Although this video clip doesn't show you the intermediary steps, he is very clear that how he has begun is essential for getting these lovely results.
The process is the same, whatever style or genre you're working in: you can only take it one step at a time.