Be natural. Throw in some stories about the flies you're tying. Why you like this pattern. What you've caught on it. Create a reason for the people watching to want to tie the fly. And, be personable. Most of the tyers we watched this weekend were personable and friendly, although a couple of fellows were quite full of themselves. People would watch for a second or two and move on, or would stand back and make comments. Also, don't be afraid to throw in comments about errors or challenges you've had while tying a pattern. I've only tied in classes publicly, but when I demonstrated canoe building I found that there were about four or five questions that were asked over and over again. Be relaxed and have fun. If you're having fun, so are those who are watching. JGW