Wear a full face helmet. My friends buddy has swelling of the brain and an unsure prognosis. He was wearing a $20 cruiser top hat pirate helmet.
Yes, I work in the motorcycle apparel and helmet industry and when people complain about the price of a helmet, I try to explain to them that it's their head they are trying to protect.
And given the fact that most helmets are warrantied for five years, you can take the price of a $500 helmet and see that you are only spending $100 per year for something that could save your life.
I must admit, however, that I rode around my neighborhood once without a helmet and felt so "free" -- it was such a crazy feeling. But after hearing, reading or watching videos of people getting into accidents, I want to be fully protected when I ride my Grom.