Here's one way to start a painting.
You could do this in oil or acrylic. In this particular case, it's an oil. And I'm using a quick-drying white - you could use Alkyd White; or Underpainting White; but this time, I'm using the remains of my lead-based Flake White, which is becoming harder and harder to lay hands on - partly thanks to European Health and Safety Regulations, but mostly because the last major manufacturers of lead chromate have shut down. So if it's going to be available in the future, it's going to be expensive - the remaining manufacturers will of course put their prices up.
Anyhow - I've got some, so I'm using it!
First, I've stained the canvas board with Burnt Sienna, diluted with Low Odour Thinners (could just as easily have been Turpentine). Then, I've drawn a basic design with a mix of Burnt Sienna and Ultramarine Blue; and then I've worked into that with the Flake White, the idea being to allow these lights to shine through paint applied on top of them - in other words, this is a means of achieving the "glazing" method in oil paint.
Over the next few days or weeks - emergency dental appointments permitting: don't ask - I shall glaze transparent colours over the top of this underpainting, which has now dried; I'll probably need several layers, increasing the amount of oil very gradually in each so I can avoid any risk of the paint cracking later. And - hugely bravely, you might think: I certainly do - I'll show the stages here and elsewhere, in the fond hope it'll all work out on the night. I may need some luck with this....