I got back from Windycon 38 last night. Windycon is a moderate sized science fiction convention in the Chicago area and is one of my "regular" conventions.
When I go to a convention I have three basic purposes. First is being there as a science fiction fan: buy stuff, listen to filk, appreciate the costuming, attend panels discussing favorite books and series, that sort of thing. From this perspective Windycon was a rousing success.
The other two purposes are from my perspective as a professional writer: meet other professionals in the field with an eye to doing business. It could be getting to know other authors who might remember you and recommend you to an anthology editor (it was that kind of personal contact that got me a chance at the Heroes in Hell series) or it might be a simple "here's the editor you need to send your story to" or it could be a "send the story to my attention and I'll take a look" from an editor or agent. (I can dream can't I.) The final purpose is to get your name in front of fans with the idea of selling books and stories. Since I now have stories in anthologies (Lawyers in Hell currently and Sword & Sorceress XXVI and Adventurers in Hell forthcoming) this is a part of getting "word of mouth" started to help sell these books.
From a professional perspective my visit to Windycon was, shall we say, less than successful. I had one programming item, a reading, but without other programming items to introduce me to congoers and my decided lack of fame in science fiction there wasn't anything to draw people to that reading. Result being that nobody showed up. Well, one person did--the individual whose job it was to go around and count how many people were attending various panels and other programming items. He hung around and we ended up adjourning to the con suite to chat.
Oh, well, you can't win them all.