At best, we get the general meaning from context, though with difficulty. At worst, a recognisable word has changed enough in meaning that we think we understand what we actually do not. As in "censure," below. Entirely different now.
Polonius's speech to Laertes. Note that we have some advantages here. It is Shakespeare's most famous play, and often considered his best. The speech itself is known even outside the context of performance and study. We don't get all the rules for thou and thee when creating speech, but we get the idea reading, because of the King James. There are common sayings that have entered the language, even cliches, near the end of the famous speech. But I submit it is a tough go.
Yet here, Laertes? Aboard, aboard, for shame! (Does he mean here in place, or time? mostly time?)
The wind sits in the shoulder of your sail (Metaphor for Laetertes' destiny, or just the physical sail?)
And you are stayed for. There, my blessing with thee. (Waited for. I think.)
And these few precepts in thy memory (...is he being quizzed on this, Polonius? Ah! You mean you are going to give him some precepts! Got it.)
Look thou character. Give thy thoughts no tongue, (No clue. Character is a good thing? I should have good character? I should look for it in others? Then, keep silent? Don't let anyone know what I'm thinking?)
Nor any unproportioned thought his act. (I'm betting an unproportioned thought is...extreme? Not thought out?)
Be thou familiar but by no means vulgar. (Be chummy, informal, but not curse or tell dirty jokes? Or does this mean to be friendly, but not with lower classes.)
Those friends thou hast, and their adoption tried, (Adoption. Waiting period on real friendship? Then you take themm for good? )
Grapple them unto thy soul with hoops of steel, (Grapple...hoops. Cling to them even if they don't like it? Or just be loyal.)
But do not dull thy palm with entertainment (Is this a masturbation joke? Or about spending money, like greasing a palm.)
Of each new-hatched, unfledged comrade. Beware (Okay new. Poetic. But is it the youth of the person or the newness of the relationship?)
Of entrance to a quarrel, but being in, (A quarrel with an individual? Between other individuals? Political or religious quarrels?)
Bear ’t that th' opposèd may beware of thee. (Don't fight unless you think you can win, or at least wound. Got it.)
Give every man thy ear but few thy voice. (So, act like a spy among your peers. Or maybe you think I should just shut up, Polonius?)
Take each man’s censure but reserve thy judgment. (So everyone can criticise and insult me without reply. Don't come to any conclusions about others, really.)
Costly thy habit as thy purse can buy, (Buy only the best wine, tobacco, restaurants. Seems like bad advice.)
But not expressed in fancy—rich, not gaudy, (Gaudy wine? You've lost me here.)
For the apparel oft proclaims the man, (Ah, clothes, clothes! Now I get it. Wear the best you can afford, so that people will think you drive a Mercedes or Volvo.)
And they in France of the best rank and station (Like the French, who are really big on this style and wealth thing.)
Are of a most select and generous chief in that. (Generous chief...you're losing me again. Are they forgiving, or disapproving?)
Neither a borrower nor a lender be, (Yeah I've heard that. Seems good)
For loan oft loses both itself and friend, (Actually, I've had that happen to me. You're right.)
And borrowing dulls the edge of husbandry. (I'm not in 4-H and not raising animals, so I'm thinking that "husbandry" is a more general term for working. And that Tom Lehrer joke occurs to me.)
This above all: to thine own self be true, (Do what I feel? Don't kid myself? Is this like my best self, a kind of Virtue Ethics?)
And it must follow, as the night the day, (Universal law. Not sure it is, though)
Thou canst not then be false to any man. (Sure I can. Watch me.)
Farewell. My blessing season this in thee. (Because you say this nicely, it is more likely to sink in.)
Most humbly do I take my leave, my lord. (Why humbly? Is something up, or is this just the usual way they talked?)
The time invites you. Go. Your servants tend. (Are we back to that sail thing at the beginning again? The time is ripe. Time is gesturing to me impatiently? The hired help is completely ready and getting itchy? What the hell?)
Farewell, Ophelia, and remember well (This is clear. Finally)
What I have said to you. (Wink wink.)
Here's a fun comparison: There is an English creole, Gullah, created by rice plantation slaves in Georgia and South Carolina. Some written work has been drawn out of it, but it is largely an oral language.* There are sill a few speakers of it. In terms of reputation for elegance, it is at the opposite end of the continuum from OMG! THE BARD! But it is just about as understandable to us now. If you went and lived among them for a few months it would be easy, just as it would be similarly easy for a time traveler to converse in the London dialect of 1600 after just a few months. We are close enough that it is a fairly straightforward adjustment.
Brer Lion bin a hunt, an eh spy Brer Goat duh leddown topper er big rock duh wuk eh mout an der chaw. Eh creep up fuh ketch um. Wen eh git close ter um eh notus um good. Brer Goat keep on chaw. Brer Lion try fuh fine out wuh Brer Goat duh eat. Eh yent see nuttne nigh um ceptin de nekked rock wuh eh duh leddown on. Brer Lion stonish. Eh wait topper Brer Goat. Brer Goat keep on chaw, an chaw, an chaw. Brer Lion cant mek de ting out, an eh come close, an eh say: "Hay! Brer Goat, wuh you duh eat?" Brer Goat skade wen Brer Lion rise up befo um, but eh keep er bole harte, an eh mek ansur: "Me duh chaw dis rock, an ef you dont leff, wen me done long um me guine eat you". Dis big wud sabe Brer Goat. Bole man git outer diffikelty way coward man lose eh life.
*Though Shakespeare wrote his works, Elizabethan English, more properly called Early Modern English, was oral as well. There were few manuscripts and actors were required to display much more power of memorisation than they do today, because they had less time, and less opportunity to refer back to manuscripts while learning lines. The audiences were not at all reliably literate. It was still largely an oral language. Some modern actors would fare well. In college, Glenn Close would attend first read-through with most of her lines already in place, and knew them all at first rehearsal. I heard others describe (with amused shock) when she had dropped a line and needed a prompt, but I never heard it myself. Not that I was there for even a quarter of her rehearsals. I have heard that Michael Caine was similarly stunning.