1. Keep two water reservoirs for cleaning your brushes. One for warm colors and one for cool. (This prevents muddiness in your palette).
2. Knowing when to let the layers on your paper dry before further progress is vital.
3. Carry pigment from the bricks to your palette, don't mix pigments in the bricks.
On technique:
1. Experiment adding water to a pigment on your palette (More water == thinner with less Saturation and vice-versa).
2. Experiment with how wet pigments interact with other wet pigments on the paper. (More water == better flow).
3. Experiment with the paper tilt direction (water flows under the force of gravity and this can be used to create a desired affect).
4. Know how to layer (i.e., 1st layer low saturation, broad areas with high water/flow, final layer is fine detail lines with low flow/higher saturation).
5. You must understand the color wheel and how pigments may mix.
I have beef with this guidance:
> let your palette and paint bricks get dirty
Keep your bricks clean: Let your palette get dirty (if you so choose).