Q:

Single word for an idiom giving advice

I'm trying to find a word referring to an idiom that gives advice (e.g. "Fake it till you make it"). "Nugget of wisdom" is kind of what I'm looking for, but I want a single word, not another idiom.
Edit: I should specify that I'm looking for a word that describes "Fake it till you make it".

A:

Pithy statements that give advice, e.g. "Fake it till you make it" (not a particularly good one, however...) are called aphorisms:

A tersely phrased statement of a truth or opinion; an adage. 

They are also known as adages, maxims, axioms, etc. 
Common aphorisms are easy to recognize, and they aren't necessarily idioms:

Actions speak louder than words.
To err is human, to forgive divine.
Necessity is the mother of invention.
Don't put all your eggs in the same basket.
People in glass houses shouldn't throw stones.

The last two are idioms. However, Fake it 'til you make it is not.

A:

There seem to be lots of words in English for accepted wisdom expressed pithily in the form of a particular situation: adage, proverb, aphorism, saw, saying, etc. Of these, 'adage' seems to express most prominently the advisory part which the questioner wants. The OED defn is: "A traditional maxim; a proverb or short statement expressing a general truth". I use 'adage' when I agree with the wisdom expressed, and 'aphorism' or 'proverb' or 'saw' or 'saying' when I am neutral about the truth of the wisdom expressed. 

