Be careful with this. Attempting to be charming in this way means you've taken one branch over an alternate branch. And at least in the U.S., very few people will be willing to tell you the costs once you've made the decision,
especially if you are
extraordinarily bad at being charming.
For example: at the beginning of "The Little Prince", the narrator describes his childhood drawing of a snake eating an elephant which he uses to test the people he meets as an adult. If the person tells him, "that is a snake eating an elephant," he knows he is safe to talk about "important" things in life. If the person instead tells him, "that is a hat," he talks about superficial things.
But it's actually worse than that, because in the book there is only a single person-- the narrator-- who is judging the character of others. But when someone attempts to "work" a room by being charming, they immediately telegraph their intentions to the entire room at once. And everyone else immediately adjusts their behavior accordingly.
And Americans will not only gloss over the inneffectual charms of others, they will actively lie to avoid the conflict of calling someone else a phony. So if you try to charm, there's no way to get trustworthy feedback on your progress.
On the other hand-- if we're discussing something I care deeply about, there is little to gain by you staring at my irises for the correct amount of time. Beautiful smile or not, at some point you're going to respond in words to what I'm saying. At that point you're either clearly demonstrating your comprehension and interest, or you are so quick-witted and devious that I probably want to get to know you anyway out of sheer fascination (at least on a short-term basis).