Allow the child to have his or her own paper and pen. Let the child add words to his or her list as you add words to yours. Have the child 'read' the list to you (it may contain scribbles, lines, and attempts at some letters which is beginning writing).
Encourage the child to help name items that you need to buy at the store. Tell him or her that you will make a list so that you can read it while you are shopping. Allow the child to see you writing so that he or she associates spoken words with written words.