Like all paint-effects, sponge painting can be a little messy, so wear old clothing or overalls.
Also: remove or cover all carpets, furniture and other valuables from the room.
Prepare the surface that is to be painted, apply at least 2 coats of mid-sheen paint in your chosen colour and allow to dry thoroughly.
Water-based paint dries quickly so start on your smallest walls first; your speed will improve with experience.
Have a bucket or bowl of clean water and some rags close at hand for cleaning purposes.
Pour a little of the thinned paint into your tray or bowl (Approximately a pint (½ Litre).
Lightly dampen the sea-sponge with water and wring out thoroughly. (Use dry for oil-based method).
Dip the sponge in the paint, and then dab it on a dry part of your tray or bowl to remove the excess paint.
Now dab it onto the surface of your cardboard to practise the effect.
The challenge of sponging is to twist the sponge in-between dabs so that each impression left by the sponge is different to next.
Only dab 6 to 8 times before reloading the sponge.
When you feel confident, try it on the walls.
Carefully clean paint from woodwork etc while you work, otherwise, re-paint woodwork etc when it is dry.
Allow the paint to dry before protecting with a coat of clear glaze or varnish. (optional).