Like vs. As

We generally use LIKE and AS to make comparisons

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LIKE
LIKE = similar to; the same as.
* He speaks like a native speaker. (= He speaks similar to a native speaker)
* She looks like a supermodel.
* You look like him.
* Stop behaving like animals!
LIKE is mainly used as a comparison.
 
AS
AS = the way; in the same way; in the same condition.
* Nobody sings as she does. (= Nobody sings in the same way she does)
* They went to the party as they were.
* Please don't use my plate as an ashtray.
* As I said before, we have to get ready.
Notice how you could replace AS with 'the way' or 'in the same way' and maintain the same meaning.
It is common in American English to use LIKE instead of AS. However, it is generally considered informal to use it in this way.
* We play football like champions do.
Another use of AS is to say what the role/position/function of a person/thing is.
* He started work as a carpenter.
* She used the tapestry as decoration in her living room.
* I worked as an English teacher at the school.
LIKE vs. AS
Be careful, in similar sentences that use LIKE and AS, the meanings of each sentence are very different. For example:
* As your boss, I must warn you to be careful. (I am your boss - I am in the role of boss - REALITY.)
* Like your boss, I must warn you to be careful. (I am not your boss, but he/she and I have a similar opinion. - COMPARISON)
Another example with different meanings:
* This curry is hot, like all good curries. 
= Similar to all good curries
* This curry is hot, as it should be. 
= Comparing to the way a curry should be.