Does your head itch? Did you just see your child scratch her head? Take a quick look in the itchy area. Any bite marks? Eggs? Live bugs? Besides these random checks, lice checks should be a part of your daily routine. I do a quick check on my kids when I brush their hair in the morning and when they brush their teeth at night. I also do a thorough combing through everyone's head each week.
What You Can Do: Understand the difference between vigilance and paranoia. Don't go crazy and grab your child's head every time they brush the hair out of their eyes. But if you see extended or repeated scratching, get in some good light, and do a check.