There’s no foolproof way to prevent blinkers in a big group, but a few techniques can help:

• Take multiple frames. With larger groups, this is still the most reliable method.
• Avoid red-eye reduction pre-flashes, which can trigger blinking before the real exposure.
• Use bounced flash if possible, since it’s less harsh and less likely to provoke blinks.
• Don’t be too predictable about the exact moment you press the shutter; some people seem to blink right on cue.
• Minimize other photographers shooting at the same time, because extra flashes can make people blink.
• A common tactic is to ask everyone to close their eyes, then open them on your count, and fire immediately as they open.

In practice, the bigger the group, the more likely someone will blink, so combining good direction with several quick shots gives you the best chance of a keeper.