To find an interesting element, drag the current time-indicator in the Layer window. Place your cursor over the element and Alt-click (Windows) or Option-click (Mac OS) to set the clone source point.

Advance the footage to a frame where you want to paint the pixels you just sampled. Then, drag in the Layer window to paint in the layer using sampled pixels from the source frame. Release the mouse, move the cursor a short distance away, and drag again to paint more of the original sample. Each stroke paints on the pixels from the source point.

(After Effects sets the duration between your clone source point and your initial stroke in the Time Shift value. When you advance the frame from your initial stroke, painted pixels change to reflect subsequent source frames. To prevent strokes from changing over time, use the Lock Source Frame option.)

Next, paint aligned clone strokes. Select Aligned in the Paint palette, and then locate a new area of interest in your footage and Alt-click (Windows) or Option-click (Mac OS) to set the clone source point.