All artists know the focal point is, of course, that thing or area in your painting to which the viewer's eye is natually drawn. It is usually obvious what and where the focal point is based on its contrast in value, color, or maybe placement.
It all has to do with focus, as in the focal point in your composition, and there should be only one. Everything else should support it by moving the eye around the painting and providing counter-balance.
However, if the focal point is too obvious, it's as if a big finger were pointing right at it so there could be no mistaking. So what is the subtle way some watercolorists have of focusing the viewer’s attention? It’s simply by painting the focal point in sharp focus or relatively sharp focus compared to other areas.
If done correctly, your eye will naturally go to the area with sharper contrast of line or color, and then move around to areas that are in less focus. It’s also effective in providing depth, I think—other areas can be out of focus s while the main attraction is in relatively sharp focus.
One acknowledged painter explained on his DVD that backgrounds, or any area that is not the focal point, should be indications of shape, light, and color. Otherwise, you run the risk of fiddling with too much detail and emphasizing things you didn’t intend.
It’s a rather simple concept really—painting the focal point in focus and everything else in less focus—but it takes forethought and planning to do it right.
Keep On Painting