Life Lessons 101 via Shakespeare

Look thou character. Give thy thoughts no tongue,
Nor any unproportion'd thought his act.
Be thou familiar, but by no means vulgar.
Those friends thou hast, and their adoption tried,
Grapple them to thy soul with hoops of steel;
But do not dull thy palm with entertainment
Of each new-hatch'd, unfledg’d comrade.  Beware
Of entrance to a quarrel but, being in,
Bear't that th' opposed may beware of thee.
Give every man thy ear, but few thy voice;
Take each man's censure, but reserve thy judgement.
Costly thy habit as thy purse can buy,
But not express'd in fancy; rich, not gaudy;
For the apparel oft proclaims the man;
And they in France of the best rank and station
Are of a most select and generous chief in that.
Neither a borrower, nor a lender be;
For loan oft loses both itself and friend,
And borrowing dulls the edge of husbandry.
This above all: to thine own self be true,
And it must follow, as the night the day,
Thou canst not then be false to any man.

But in simple English....

Don't say what you're thinking, and don't be too quick to act on what you think.
Be friendly to people but don't overdo it.
Once you've tested out your friends and found them trustworthy, hold onto them.
But don't waste your time shaking hands with every new guy you meet.
Don't be quick to pick a fight, but once you're in one, hold your own.
Listen to many people, but talk to few.
Hear everyone's opinion, but reserve your judgment.
Spend all you can afford on clothes, but make sure they're quality, not flashy, since clothes make the man.
Don't borrow money and don't lend it, since when you lend to a friend, you often lose the friendship as well as the money, and borrowing turns a person into a spendthrift.
And, above all, be true to yourself. Then you won't be false to anybody else.

Even from back in the day, these lessons still speak truth.