Plaster

Use a plastic screw anchor or a nylon toggle, which expands on the inside when the screw is tightened.

Drill a hole with the same diameter as the anchor, which should be gently pushed or hammered into the hole.

For heavier objects meant to take more weight, you should not use a plastic screw anchor or nylon toggle in a plaster wall. The best method of mounting in this case is to use a wood screw going into a beam or a "stud" behind the plaster.