As and like are often confused since they are both used to compare actions or situations. There are, however, important differences.

As

We use as to talk about job or function.

• I worked as a shop assistant for 2 years when I was a student.
• He used his shoe as a hammer to hang the picture up.

In comparisons, the structure ‘as adjective as’ is often used.

• He’s not as tall as his brother
• She ran as fast as she could.

In the following comparisons as is a conjunction – it’s followed by a clause with a subject and a verb.

• He went to Cambridge University, as his father had before him.
• She’s a talented writer, as most of her family are.

Like

In the following comparisons, like is a preposition and it’s followed by a noun or a pronoun.

• I’ve been working like a dog all afternoon.
• None of my brothers are much like me.
• She looks just like her mother.

Like and As if/As though

Like, as if and as though can all be used to make comparisons. There is no difference in meaning among the 3 forms.

• You look as if you’ve seen a ghost.
• You talk as though we’re never going to see each other again.
• It looks like it’s going to rain.

Expressions with ‘as’

The following expressions all use as.

• As you know, classes restart on January 15th.
• I tried using salt as you suggested but the stain still didn’t come out.
• As we agreed the company will be split 50/50 between us.
• Their house is the same as ours.

(British Council. As and Like. Retrieved October 2, 2012, from http://learnenglish.britishcouncil.org/en/grammar-reference/and)