As your teacher, I want you to do the homework. (I'm your teacher.) Like your teacher, I want you to do the homework. (I'm your sister, but I want you to do the homework. Your teacher wants this too.) Details: http://learnenglish.britishcouncil.org/en/grammar-reference/and

One of the way to differentiate between "like" and "as" is to use "like" when no verb follows. For example: He jumps like a rabbit. But if the clause that comes next includes a verb then you should use "as". For example: He jumps as if he were a rabbit. More examples: - Mary looks like a princess. - It's as if Mary thinks she is a princess.