Look for helmets certified by safety-testing organizations like ANSI, SNELL, or CPSC—or preferably all three—to confirm they have passed safety tests.
Some helmets come with a short visor, sometimes removable, which has no effect on safety. Be sure it isn’t blocking your ability to see forward when in the riding position.
For the gravity crowd doing stunts and jumps on ramps and obstacles, a multi-impact helmet is a better choice. This type of helmet is thicker-shelled, impact-intensive and is built heavier and less ventilated. These helmets also used by skateboarders. They look a lot like a bowling ball, only with a few more holes!
The helmet should fit level on your head, not in your eyesight or tilted back like a beanie or beret!
To avoid headaches, the shell—the hard part—should fit close to your head without any tight pressure points. (Modern helmets have retention devices that hug the helmet to your head and keep it stable while riding. Some have a dial that adjusts this tension, or Velcro or elastic elements.)
For eyeglass and sunglass wearers, be sure the helmet and glasses don’t interfere with one-another. The pros put their eyeglasses around their helmet straps, not under. This keeps the straps from pushing the sides of your sunglasses into your head when the straps are sufficiently tight.
The helmet straps need to meet on the sides of your face at your jawbone, below your earlobes, and clasp under your chin as snugly as you can comfortably wear it in a riding position. Generally, you’ll be able to slide two fingers between the strap and your chin.