Watercolours:

Quinacridone magenta

Cobalt blue

Ultramarine blue

Winsor blue(green shade) or Phthalo blue

Transparent yellow

Burnt Sienna

Brushes:
Size 6 or 8 round

Rigger or fine size 4 brush

Watercolour paper:
140lb NOT watercolour paper approx size 28 x 38 cms

Misc: 

B Pencil

Pebeo masking fluid plus applicator

fine wax crayon(optional)

Sketch the scene out lightly, with not too much detail.

Using either a small wax candle or a fine twig mask out highlights on the trees. The sketching of the foreground bluebells can be left until later.

Prepare a pool of pink-mauve (Quinacridone magenta and Cobalt blue) and a blue-mauve, with the same two colours but with more blue in the mix and a yellow-green (Transparent yellow and Cobalt blue) and a blue green, (Winsor blue (green shade) plus Transparent yellow)
Wet the lower area of paper, from just above the distant bluebell line.
Using a size 8 brush apply pink–mauve first followed by blue-mauve,leaving gaps between for green. Bear in mind where you wish a path to lead into the picture. Apply yellow- green then blue-green.

Dry. Wet wooded area and drop in areas of Cobalt blue, followed by the yellow–green mix. Vary the intensity of the green and stipple in stronger areas using a slightly creamier consistency. See step 4

Whilst still damp stipple in the blue-green mix with the point or top edge of the brush to give depth to the shadowed areas.
When dry splash a few finer speckles of paint using a stronger mix.

Mix a pool of brown, Burnt Sienna plus Ultramarine with a dash of yellow to make it a slightly greenish brown. With a finer size 6 brush work wet on dry drawing the brush from the base of the trunk upwards. Add water to diffuse and make paler tones on the lighter side. Add a stronger mauve shade on the deeper and shadowed sides of the trunks ,Quinacridone magenta and Ultramarine. Dilute paint for distant trees.

Remove masking fluid and using fine brush or rigger add fine branches. Add a little of the mauve mix in the lower area of the woodland just above the horizon to give density.

Refer to the photo, alternatively pick a few bluebells and position them on the paper to plan composition.

With pencil indicate the simple bell shape. Add a dash of yellow for the anthers and working wet on dry commence with a pink–mauve base followed by a blue-mauve, letting the colours merge wet on wet. Use the point of the brush to suggest the curled petals. Introduce a little Winsor–blue green shade.

When dry add some definition with stronger shades, whilst considering the shadowed side of the bell.
Add stems with a mix of Transparent yellow and Ultramarine. Drop in a purple mix towards the top of the stem and on shadowed side.

Using a stronger mix of green stipple a little more depth in the woodland foliage and a mid shade of purple using the tip of the size 6 brush to add downward brushstrokes to suggest the texture of the bluebells. Soften brushstrokes here and there and add more strength of colour. A touch of yellow in the mauve gives a deeper shadowed tone.
Suggest larger silhouette shapes of the bluebells nearer the foreground

Add the green areas, a hint of a path leading in, and a little texture here and there and the foliage in the foreground.