Blinking happens, that's why we take lots of photos haha.
If it happens a lot, your eyes might be dry or irritated from contacts/dust in the air. Eyes drops can help. Keep your eyes relaxed and have plenty of rest
I usually use this technique for group photos to have everyone's eyes open - get in your pose and be ready, let the photog make whatever adjustments. Then close your eyes, let the photog count down and open when he says for the shot.
You can call me Jono
San Diego Comic-Con, Otakon, Dragon*Con