Claim
A round is a promise, so join it or stay out cleanly
Buying in rounds only works because everyone expects to buy one. The awkwardness comes from men who accept three and buy none, and from men who buy the first and leave before their turn comes back without saying anything.
Two clean positions. Join, and remember that your round is a debt that gets called. Or opt out at the start with one sentence: I am going to get my own tonight. Nobody minds the second one when it is said early, and everybody notices it at the end of the evening. The convention is about predictability rather than fairness in currency.
Claim
Pour for others, and never top up without asking
At a table with bottles, serving other people before yourself is the entire etiquette, and it holds across most cultures even where the details differ.
The one rule men break constantly, with good intentions, is refilling a glass without being asked. It removes the only tool the other person has for controlling their own intake, because a man who is trying to stop at two cannot stop if his glass keeps returning to full. Ask, wait for the answer, and accept a no without a second offer. Whoever is pouring is effectively setting everyone else pace, and doing that by default rather than by consent is the discourtesy.
Action
Order wine in a restaurant without theater
Three sentences will do the whole job. Tell the waiter roughly what you want and what you will spend: we are having the fish, something dry and white, around this price, pointing at the list rather than saying a number aloud. Ask what they would pick. Take the recommendation.
The tasting ritual is not a quality judgment and never was. You are checking for a fault, meaning cork taint or oxidation, which smells like wet cardboard or vinegar. That is the only reason to send a bottle back. Not liking a wine you chose is not a fault, and saying so puts the restaurant in an impossible position.
Evidence
Toasting rules are local and specific
This is the area where confident improvisation goes wrong fastest, because the rules are precise and vary. Look at whoever is hosting and copy them.
Some patterns worth knowing: in much of central and eastern Europe, eye contact during the toast is expected and its absence is noticed. In Japan, pouring for others and letting someone pour for you is part of the interaction, and pouring your own is a small oddity. In a formal dinner with speeches, nobody drinks before the host has toasted. And glasses raised with a non-alcoholic drink count exactly the same everywhere, which matters for day 6.
Example
At a supplier dinner in Warsaw, Greg was the only person at the table who kept looking at his glass rather than at the person toasting. Three toasts in, the host mentioned it, pleasantly, and Greg spent the rest of the evening making eye contact.
He got it wrong because nobody had told him, which is the normal way this happens. What he did right was to fix it immediately and without a speech about cultural differences. The etiquette course principle applies: a man who adjusts quietly costs the table nothing, and a man who explains at length that he did not know costs everyone ten minutes.
Caution
The things a room actually notices
Not your knowledge of grapes. Four behaviors, all watched closely and all avoidable. Pressuring anyone to drink, including with jokes. Ordering the expensive bottle when someone else is paying without checking first. Being noticeably further along than everyone else. And how you speak to the staff, which as at any table is the most reliable public information about you available.
One more that costs men their reputation quietly at work events: telling someone what they said last time they drank. Whatever happened, the man who brings it up in front of others is the problem, not the man who said it.
Aside
Where drinking etiquette stops being etiquette
All of this assumes a room where everyone is broadly in control. Some rooms are not, and in those the polite conventions become tools for pressure: the round that obliges a fifth drink, the toast that cannot be refused, the boss who fills glasses.
When that happens, the convention is the thing to break. It is always correct to stop drinking mid-evening, to leave without explanation, and to put a hand over a glass. Nothing in any tradition obliges you to keep pace with a room, and any custom that requires it is being used rather than followed. Day 6 gives you the sentences.