Like (when used to mean "similar to") is a preposition. As (when used to mean "in the same manner") is a conjunction. Prepositions govern nouns, pronouns, and words used as nouns. Conjunctions join clauses.
So, "Like Pan, I'm an orangatan." But, "Pan behaves as a good orangatan should behave."
Basically, if a subject and verb are to follow, use "as." If a single word foll