That could be very cool. What color are you using? Are you going from the ceiling light to dark or dark to light?
First of all tape off any edges around doors or cornice and ceiling. Then paint a neutral colour. Dry.
Then chose three or four colours of paint from the same colour paint sample chart. So they vary in different shades of the same colour.
Then decide whether you are doing dark to light going up or from the top down.
Once you have decided. Start with the dark paint with a brush or roller, and paint until you are approximately a third of the way down or up depending on you. Then leave approximately 20 - 30 cm plain. Then under this plain paint again but use the next shade that is slightly lighter. Then leave a plain strip again.
Then use the last colour. You should now have three varying colour stripes with two blank spaces between.
Now for the blending.
Mix some of the dark and the next shade together, make sure there is enough to paint in the plain space between the two darker shades on the wall. Now with a wet brush paint the plain space, blending within the two colours.
Then mix the middle shade with the lighter shade and do the same in the next plain space.
Hope this is clear enough.
Get a one coat paint for better results. And it should be a wipeable paint as If it marks it will be hard to get the right colour blended mix again.