Developing range of tones

Have never had enough sketches that help to scaffold my painting of landscapes in past. Have undertaken some studies in several mediums and these have helped. However I can become too 'tight' and detailed at times thereby losing the vibrancy and dynamism that attracted me to the subject/object.
Looked RA painter Ken Howard's 'Dora,summer interior, Cornwall, 2009 (Image pasted in Exhibition Visits logbook) and 'Silver still life', Chelsea, at http://www.richard-green.com/

Evaluation: counted tones and tints where light and shade is cast in partic and also looked to where the same tones and tints used throughout painting. At least 5 - 7 tones with succint, powerful and at times subtle use of contrast. Just delicious use of paint.Reminds me that the juxtaposition of tones is a key factor.
Next steps:

• draw many more objects and still subjects in sketchbook (tend to use A1 for fugures as it's effective for me) to develop tonal range so that I interpret and represent more precisely rather than rely on lines where tones would say more.
• look again at tonal range used in assignment painting after a short period of time has elapsed.
• Ask myself if juxtaposition of tones and highlights could be bettered.