Tonal Studies
The distribution and values of your darks and light tones will contribute probably more than anything else to the success of your painting. Try to see the composition in grey tones and forget for the moment the colour.
Take your sketch pad and quickly rough in several quick sketches don’t make them too large 10 x 7 cm is fine. I draw an outline frame first leaving some white space around the sketch, this means if you are not happy with the composition you can add another section on any of the 4 sides (there’s nothing worse than running out of space at the edge of your pad).
Sketch from different viewpoints and quickly allow yourself 5 minutes per sketch, this will force you to think quickly. Look only at the overall shapes don’t add any detail for the moment. A very useful piece of kit is a red photographic filter, when you view your scene through it you only see tones and it’s easy to see which colours are actually the same tone and which are lighter/darker. I use Progressos you can buy them in any hardness I love my 8B.
Here are 6 studies using only 3 tones each