Hamlet Critica Lreview

1. "Give thy thoughts no tongue, nor any unproportioned thought his act"
Polonius tells Laertes not to speak his mind, nor to act without thinking properly first. Ironically, Polonius breaks both of these rules himself, the first through his manner of speaking, and the second most notably through hiding in Gertrude's chamber to spy on Hamlet.
2. "Be thou familiar, but by no means vulgar"
Polonius is telling Laertes to be friendly and colloquial, but not to be overly vulgar as a way of impressing people.
3. "Those friends thou hast, and their adoption tried, grapple them to thy soul with hoops of steel;"
This could be interpreted as "if you have a good friend, hold onto them".
4. " But do not dull thy palm with entertainment of each new-hatch'd, unfledged comrade"
Polonius discourages Laertes from going out of his way to entertain new friends.
5. "Beware of entrance to a quarrel, but being in, bear't that the opposed may beware of thee"
Polonius advices his son to stay out of fights, but should he find himself in one it is important to keep his opponent afraid of him.
6. "Give every man thy ear, but few thy voice"
Laertes should listen to everyone, but should be careful about with whom he chooses to vocalize agreement. 
7. "Take each man's censure, but reserve thy judgment"
Laertes should consider any criticism he has, but not be quick to criticize others. 
8. "Costly thy habit as thy purse can buy, but not express'd in fancy; rich, not gaudy;"
Polonius advises Laertes to buy the best clothes he can buy, but to buy clothes of genuine quality rather than simply flashy ones.
9. "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" Polonius tells his son that a man's clothing can say a lot about his character, and that the French pay a lot of attention to what people wear.
10. "Neither a borrower nor a lender be; for loan oft loses both itself and friend, and borrowing...