From the Painting Guide: Everything considered, for me what these paintings lack is depth. If you look at Country Lane, your eye is nicely led in by the composition along the path, but the tone remains the same from foreground to middle ground. Squint at the painting and you'll see that the grass and trees in the background blend into one dark tonal area, while the path and the sky blend into a light one. This makes the scene appear flat, without a sense of one walking into the distance.

Squint at Covered Bridge and you'll again find many of the elements are the same tone (the foreground, the bridge, the trees). You've got that really strong shadow on the inside of the bridge, yet the shadow from the bridge itself on the pillar on the opposite side of the river is quite pale. I'd imagine there could also be some really dark shadows in the creeper growing over the stone wall. Look again at the tone of the tree trunks that stick out below the bridge, which are much lighter than the bits above the bridge. It's a range of tones that creates depth, not just composition or colour.

What I would suggest you do is a tonal exercise, using just black and white paint initially. Set up a still life with a few simple objects and a strong light source from the side (to create shadows). Take a grey sheet of paper, or mix a mid-grey and cover a sheet with it evenly. Now paint in the strong darks of the subject in black, then the strong lights in white. Now mix two greys, one lighter than the background and one darker, and use these for intermediate tones in your painting, leaving the mid-tones as the grey of the paper. You'll now have five tones in your painting and should be able to see how it's tone that creates depth. The next step is to repeat the exercise using colour, but remembering to think about tone as well as colour, so for example on just how dark a green it is rather than just that it's a green.

Try reworking Country Lane with greater contrasts between light and dark, for example darken the shadow side of the tree trunk, where you've painted the shadow on the grass. Make the shadow of the grass on the path deeper (darker) right next to the edge of the grass. Make the shadows under the trees at the back darker. As an approach, try exaggerating the contrasts, so making the darks really dark and the lights really light, and then working in from here, rather than starting with a mid-tone and then darkening or lightening.