How could a person write a paragraph on the topic "If I were a pencil"?
Begin by thinking of the physical characteristics of a pencil. It is made of wood; it contains graphite; it usually has an eraser on it; it must be sharpened to be of any use.
Now think of ways in which the pencil is used: to write; to draw; to doodle; to drum on a desk when you're bored; to twist between your fingers like a twirler twists a baton.
Try to imagine that you are the pencil itself. You can talk about all the characteristics above. You can also talk about being lost easily, or kept at the bottom of a dirty purse or back pack. Maybe you can talk about the fact that you will be thrown away when your owner learns to write with a pen more than a pencil.
Use these ideas as a beginning place for your own imagination. You should now be able to write that paragraph very well and very easily.