What is the goal of Mark Twain's "Advice to Youth"?

Mark Twain's satiric graduation speech mocks the graduation-speech genre that most often feeds young people lies and platitudes. He does this with the moral goal of mocking and shocking people into awareness of their own hypocrisy.

In this speech, the speaker advises hypocrisy. For example, he states,

Always obey your parents, when they are present.

He also advises his audience to learn the "graceful and beautiful" art of lying early:

An awkward, feeble, leaky lie is a thing which you ought to make it your unceasing study to avoid.

Twain uses hyperbole or exaggeration, a hallmark of satire, to make us laugh and to point out the failings of his society. For example, he uses it not only to attack hypocrisy but also to target the violence American life. He advises young graduates who have been offended by someone merely to hit them over the head with a brick rather than using dynamite. He also advises that they be careful with guns.

Tongue in cheek, Twain also slips self-promotion into his speech when he recommends his own book The Innocent Abroad in a short list of pious sermons he advises reading. Not only does he plug himself, he points to a book of his that further dissects human nature. Finally, Twain ends with these words:

Build your character thoughtfully and painstakingly upon these precepts, and by and by, when you have got it built, you will be surprised and gratified to see how nicely and sharply it resembles everybody else's.

This statement shows that Twain is well aware of how adults really behave under the pieties they mouth to the young. He hopes that if adults can see themselves in this mirror, they might want to change.

What is Mark Twain's central idea in "Advice to Youth"?

Is it not amazing that anyone would ask Mark Twain, America's curmudgeon, to address a group of young girls?  As so cogently put on the site listed below, it did, indeed, "turn the conventional moral lecture on its head."

Yet, in his satire--as is usually the case with satire--Twain does give some solid moral advice.  The main point is what the previous poster has succinctly written, conventional wisdom is often hypocritical and phony:  Getting up with the lark does not make one a better person, obeying one's parents simply because they are the parents teaches nothing, the truth does not always prevail, and guns do not always kill people.

If, however, one understands Twain's satire, one realizes that he--perhaps more than many others--truly believes in moral behavior, for he quips that he has not learned how to "practice this gracious and beautiful art."  And art it is, not reality.  The perspicacious listener, then, would have discerned this valuable lesson and long remembered it, as is usually the case with satire.

In my opinion, the main idea of this essay or lecture is that conventional morality and conventional sermons about morality are totally worthless.  This is a theme that Twain explores in books such as The Adventures of Huckleberry Finn and I believe he is doing it again here.

I think he is saying that conventional sermons and the morality they are trying to pass along are sanctimonious and fake.  I think he is trying to tell people that they should think for themselves rather than just swallowing the moral lessons that they are given by their parents, teachers, and so on.