Advanced Clone Brushery
The Clone tool works best in small areas because you can start to see a repetitive pattern in the photo if you paint over too large a region. But to help you out, the Clone tool has two different modes, which you control via the Aligned checkbox in the toolbar at the top of the Photoshop Elements screen. In one mode, when you pick up the brush and paint elsewhere, the source stays where you put it; this is called Nonaligned mode. If you pick up the brush and start painting elsewhere, and the source moves the same relative distance from where you started, your tool is in the Aligned mode.
It's kind of a complicated concept, but you can see what I mean if you try cloning someone's face and then painting it somewhere else in the photo, as I did here. If you clone it using Aligned mode, you can paint the entire face without any glitches even if you paint a few strokes, lift and move the mouse, then click and paint again. Try that in Nonaligned mode, though, and you'll restart the face from the clone source point wherever you click, making it impossible to paint a face unless you do it in a single set of strokes without lifting your finger off the mouse button. Some pictures work better with one mode or the other--experiment to see which is best in each situation.