An observation about cons, reenforced by this weekend's Boskone: Con guests are there for the fans and readers, not the other way around.
Sure, writers and artists and game designers attend cons to promote our work, but it seems to me that most of this promotion should be in the form of "content marketing," aka offering something of value. That means trying to figure out why the people in the room chose to attend that particular panel or event, and addressing the needs and interests that brought them there. Are they seeking information, entertainment, community, connection? The best guest cons, imo, are people who ask themselves these questions and come up with a more compelling response than, "Buy mah books!"
Point in case: I was not familiar with Hillary Monahan's work before October 2017, when I attended a book festival in northern Massachusetts. She was on a panel with perhaps a half dozen other writers, and she made a stronger impression than all the rest combined. She didn't monopolize the conversation, and she addressed questions in a concise and articulate manner. Nothing off-topic, no omg-how-I-love-the-sound-of-my-own-voice rambling. She was the only one who appeared to be actively listening when other writers spoke. Everyone else gave the impression that they were thinking about what they wanted to say next and impatiently waiting for their next chance to talk. She named her books when asked about them and attempted to tailor her recommendations to the interests of the person asking, but she was more likely to talk about other writers in the genre. She came across as authentic, intense, and passionate about books in generaI; in short, the sort of person who's likely to write books I want to read. I bought one of her books that day, read it that night, and ordered more. I am now a huge fan and will read anything she writes from this point on. But I don't even remember the names of anyone else on that panel, even though several of them probably had more air time.
That, imo, is how to approach a con. Be authentic, be generous, be connected. Don't float through the con in a bubble of your own self-importance or, which is even more likely, your insecurity.
For an extreme introvert, as many of us are, that can be a tall order. I suspect that a great deal of the rambling and the monopolizing and the apparent self-importance are the result of overcompensating by people who would be far happier and more comfortable if we were back in our caves, madly writing.
What this comes down to, I think, is that being an effective con guest is a skill set, one of many that writers need to acquire. I'm definitely not there yet, but I come away from each con with a list of observations and ideas for improvement.