This one is quick and not good, but I'm getting better with using Holbein's Acryla Gouache paint. The technique is actually really similar to using a full palette frottis ebauche in oil painting.
From what I've seen from Studio Ghibli, they start their backgrounds loosely with large brushes and then they finish the detail. Working broad to narrow has roots in every form of painting.
Anyone interested in background painting for animation should check out this video: