Taken at face value, Polonius give Laertes some excellent advice in regards to how to present himself to the world. Polonius's ultimate point with both of his children is that they need to be careful in the way they act because their actions become their reputation, and Polonius doesn't want any negative actions to reflect badly on the family name. To this end, he brings up a lot relevant topics. He starts by telling Laertes to "look [to his] character" by giving "thy thoughts no tongue." He wants Laertes to keep his opinions to himself and not act like a big mouth or a know-it-all. He reiterates these ideas later when he says, "Give every man thine ear, but few they voice" and again when he tells Laertes to "take each man's censure, but reserve thy judgement."He next tells him to be "familiar, but by no means vulgar." He is encouraging Laertes to be friendly, but not overly friendly or in any way inappropriate. He encourages him to gather good and trusted friends closely like with "a hoop of steel," but not to accept everyone he meets with that measure of closeness. In terms of his interactions he warns Laertes to stay out of quarrels in the first place, but if he is in one he should still never forget himself; people are always watching.
Polonius even address the more superficial aspect of clothing by telling him to dress nicely, but not in a flashy or gaudy fashion.
Near the end of the speech he utters the now famous line: "neither a borrower nor a lender be / for loan oft loses both itself and friend."
He concludes with a comment that could be read as a contradiction to all of the previous advice. He tells Laertes "This above all: to thine own self be true." If one only reads that line, then it would seem he is telling Laertes to do whatever seems suits his nature. The problem with that reading is that it ignores the rest of the statement. Polonius concludes the thought by saying that if you are true to yourself (meaning you put yourself and your reputation first) then "thou canst not then be false to any man." THAT makes sense to the overall intention of Polonius's speech. Polonius wants Laertes to always be aware of his actions and to live a most righteous and cautious life because that will ensure that his reputation will always be above reproach.