Is it true that I should have a focal point - that something should be unique so the viewer focuses his attention there?

There is always going to be a focal point in a painting. The focal point is what the viewer sees first. Often, however, there needs to be additional focal points within the painting, instead of just one. Drawing the viewer's eye away from the focal point, to discover, explore and be surprised by other areas in the painting creates interest and often adds to the strength of the painting. A focal point that is surrounded by additional points of interest, or elements to discover keeps the viewer engaged longer, absorbing detail by detail.