For a strong composition, you want the values to be in quite different amounts, not similar.
Try this rule to start: two-thirds, one-third, and a little bit.
— Marion Boddy-Evans
This is a quick way to see if a painting will pull it off, without having to spend time on a painting that lacks contrast or composition or something else…
In a sketchbook, I created a thumbnail about 2″ x 2″. I quickly sketched the shapes (not the textures) and then created a low, mid and high-value tone painting, with only one colour. In this instance, I used Payne’s Grey as it is capable of very dark values and very light values. It is also quite staining. I painted over the entire area with the lightest of values, reserving the whites, and then painted over with the mid and darker values. I can now see where some darks should be darker and where lights are necessary. The second door on the left-hand side should have a darker value but everything else seems about right. So next step is to draw it on full-size watercolour paper and then paint it.
By the way, I am totally loving my retirement! When I wake up in the mornings, I still cannot believe it! After having worked all of my life on one job and another for over 50 years, mostly full-time, some part-time, some jobs that I totally hated and some that I loved, to now have the luxury of time, I am grateful!!! And the best job that I ever had was teaching for 27 years in the public sector and the best employer was Cégep John Abbott College for 21 years!

Paper: Moleskine Sketchbook #25
Colour: W&N Payne’s Grey
Ink: Noodler’s Lexington Grey
Fountain Pen: Pilot Penmanship, Clear, EF Nib, Japan (8$) bought at http://www.JetPens.com