I have some flashcards for senses.  One set is "looks."
 
That looks cute.
That looks scary.
That looks beautiful.
...
That looks like an elephant.
That looks like a butterfly. 
I use those to introduce 'like' as a simile.  The you can just run with it if you have other pictures of things that look like something else.  Just try googling "cloud + *animal" or look for some hidden images like these: 
http://www.coolbubble.com/features/h...dex.asp?page=0 
I have a few children's books with these kinds of images.  "Run Away Bunny" comes to mind.  I use the books and ask first 'What's this?" - "Right, it's a boat."
What does it look like?" - "Right, it looks like a rabbit." 
Then let them try drawing some scenes.  Once they have finished have them explain their pictures.  As you advance on you can have them draw more abstract concept pictures:
a man that looks like he lost something
a boy that looks like he's hurt
a snake that looks like it has eaten an elephant
a tree that looks like it is going to attack