- When there are too many people on one panel: Panels of more than three people are fraught with peril for the speaker and the audience. You've got to allow extra time for introductions and Q&A, and, knowing they have diminished time, many speakers will simply talk past the limit. (I once had an organizer ask me to join a panel of 8, and each of us were to get 2.5 minutes to speak. No way!) If you're tempted: Ask yourself what value you can add in such a short time slot.
- When the format's prescribed too tightly: If you prefer being able to walk around the room instead of stand behind a lectern, take questions at the top rather than the bottom of the presentation, or any other variation on the standard, be sure the organizers know that and can accommodate it. If the format's already determined for you, think through whether it really meets your needs and lets you shine.
- When there's not enough time to prepare: On a few occasions--including one of my best talks--I've been asked to step in at the very last moment, and I have. (To find out how to pull this off, read "Speaker on Ice: When you need to wing it.") I'm more concerned when the call comes in advance, but only just barely (say, 3 days before or 2 days before). Typically, that means another speaker has cancelled, or the organizers didn't plan far enough in advance. Do you want to give up your preparation time? Think twice before you say yes.
- When the subject changes without notice or isn't clearly established: This is a clear sign that the organizers aren't taking good care of their speaker. I've had a few speaking invitations pegged to a specific topic, then found out it had changed after I accepted--without hearing directly from the organizers. Be sure you take the time to reevaluate if changes are made, and feel free to say "I think you'll need to find another speaker."
- When the preliminary negotiations go on for longer than your talk: You should expect to spend time talking to the organizers about how the talk will go, audiovisual equipment needs and the audience in advance. But if the logistics, location, topic, length and other basics keep changing and changing yet again, you may find it's a sign that the group's too disorganized--and disrespectful of your time. Again, feel free to say "I think you'll need to find another speaker."
- When it's not your area of expertise: Be honest and say so. You may be a good speaker and liked by the group, but don't stretch past your knowledge base. Consider, too, that good speakers often are asked to fill in when they're not experts, just to get someone to fill in--so don't set yourself up to fail. Say no.
- When your schedule gets in the way of success: You may have a clear calendar on the morning of your talk--but if you're traveling all night right before you go on, and jet lag's a problem for you, say no. Don't pile on when you know you'll be tired, rushed or otherwise not at your best.
(This post is an update of one that appeared earlier.)