Your helmet should:
- fit snug, yet comfortably
- sit on your head 2 finger-widths above your eyebrows
- should pull down when you yawn
- be replaced after any crash
Helmet basics. Website readers can have the contents to read them by clicking the “listen” icon
http://kidshealth.org/parent/firstaid_safe/outdoor/bike_safety.html#
This link shows easy diagrams of how to fit a helmet properly:
http://www.nhtsa.gov/people/injury/pedbimot/bike/EasyStepsWeb/index.htm