Like/As if

Here is a very helpful post from Triangle Grammar Guide on the use of like and as if:

Write as if you know what you are doing

"Like" is a preposition and should not be used at the beginning of a clause. Here is an example I encountered in my editing recently: The two friends look like they’d be more at home knocking the stuffing out of people on a football field. I changed that "like" to "as if." I seem to do that a lot, so it occurs to me that writers either don't know the correct usage or are deliberately ignoring it in favor of "conversational" writing.

John Bremner in "Words on Words" has a clear rule for determining whether to use "like" or "as/as if." Remember that "like" means "similar to" or "similarly to." Substitute "similar to" in the sentence above: The two friends look similar to they’d be more at home knocking the stuffing out of people on a football field. You can see that how wrong that is or hear how incorrect it sounds.

The post clears up for me the difference between like and as if in a way that helps me understand how the words differ in use.