When to Use Like, When to Use As
The proper way to differentiate between like and as is to use like when no verb follows (2). For example, Squiggly throws like a raccoon or It acted just like my computer. Notice that when I use like, the words that come after are generally simple. A raccoon and my computer are the objects of the preposition.
If the clause that comes next includes a verb, then you should use as. For example, Squiggly throws as if he were a raccoon or It acted just as I would expect my computer to behave. Notice that when I use as, the words that come after tend to be more complex.
You generally hear like used in everyday speech, so that helps me remember that like is the simpler word—or at least it is followed by simpler words. As sounds stuffier and is followed by a more complex clause that contains a verb.
Grammar Girl : Like Versus As :: Quick and Dirty Tips ™