[susan53]

Draw the beginning of a line drawing on the board. Ss try and guess what the picture is going to be - eg if you've drawn a circle : I think it's a face, I think it's the sun, I think it's a ball etc. Add another small part of the drawing - they go on guessing, add another part - and so on until you have completed the picture.
Some things you can draw : a house, a bicycle, a pair of glasses, a car - Google "blackboard drawing" for sites which show you how to do simple drawings.