For me its not always about choosing a pretty picture to create a painting but sometimes I have to get out of my comfort zone and find something that will give a challenge.
Up pops an image from a sharing site that was all in gray but with ever so many complex shapes and I knew immediately I would have it on my to do list.
This is really where the advice "don't think of the subject but just the shape and value as you see it" and this certainly HAD TO WORK for me as I had absolutely no idea what I was painting and that was the challenge.
I turned my board around as I painted sections ensuring of course that my reference image was turned too!
This complex painting took over a week of many sessions to finish but when I stood back from it the engine parts looked as they should so challenge accomplished.
Tip: every now and then find something that really gives you a challenge, your observation skills, brush strokes and though process will all improve.
Take time to carefully prepare your drawing
Choose your colours
Follow values and just paint shapes.