This is a really fun exercise using a big brush and completely limiting the amount of brush strokes used. A household paintbrush will do if you don't have anything more professional.
It's worth painting onto a coloured ground (ie an undercoat). Landscapes look great on a warm coloured ground , it could be a wash of Burnt Sienna, a pink or an orangey scarlet.
With a thick dollop of paint on a big brush the canvas is touched only once with each colour, the brush can be moved around the canvas in any direction but if it's taken off the canvas, it counts as one stroke and it's time for the next colour! It produces surprisingly effective results...
If the painting looks too unfinished, 12 more colours can be mixed using variations and tones of the colours already used and 12 more brushstrokes can be done with a smaller brush. If you STILL feel it looks too unfinished, repeat...ad infinitum. A perfectly good technique for an expressive and more abstracted piece of art!