Wet in wet washes: Mix small puddles of three or four colors which would look harmonious together. Don’t add too much of water, they should be of thicker consistency than that of those colors you had used in the basic washes. Wet the area of paper you want to paint on with a flat brush. Use clean water and see that it is evenly wet with no pools or dry areas. Wait for a second or two as the water gets absorbed into the paper. Quickly start dropping in the colors. Donot stroke too much, let the water on the paper pull the paint from the brush. Quickly rinse and blot brush in between colors or use separate brushes for different colors. If the paper starts to lose its shine, stop adding any more colors. Tilt the paper in different directions to allow the paints to mix.
You have less control over the final look than the wet on dry method but it is more spontaneous and fun and it always a surprise to see how it will turn out. This technique is generally used for background washes since the soft, out-of-focus effect gives the illusion of receding into the background, pushing the foreground subject to the front.
In the left hand side of the sample below, the back run (orange) is caused by uneven wetting of the paper. On the right hand side, the paper had begun to lose its sheen (sheen is the reflection of light caused by water on the paper surface when it is wetted) before the colors were dropped, leading to the colors staying put and not getting blended.
Dry Brush technique: You have a lot of control over this method. Take an inexpensive or old medium round brush, wet in water and blot on a tissue till it is just very slightly damp. Pick up a color in which only a drop of water has been mixed. Drag the belly of the brush over the surface of the paper, without pressing in. The ‘valleys’ in the paper donot catch the paint and they remain white. If you have chosen blue, this effect will look like sunlight on the surface of water. With a flat brush, you can do the same. Spread out the bristles a little bit and paint with a shade of brown from top to bottom. Repeat with other shades of grey and brown, and you get the texture which resembles that of wood. Experiment with different brushes and colors. Sand can be painted with shades of raw sienna and brown. Little twigs and branches can also be painted with a dry brush as they are ragged and often donot appear as continuous lines in nature. Take a small number round brush loaded with paint that is of very thick consistency and paint quick strokes with it on a dry paper. Dry brush technique is even more pronounced on Rough watercolor paper but will hardly be visible on a HP sheet.