First wave of gentrifiers are the artists, musicians, photographers, writers....white people slumming it. They'll move to the hood when its still the hood. They make the hood "cool" and "edgy" to other white people who were still scared to come before.
Second wave of gentrifiers are the hipsters....young white kids rebelling against their stale suburban upbringing and their rich parents. When a starbucks and a trader joes/whole foods comes to the neighborhood, the hipsters are close behind. With the artists and musicians' seal of approval, the hipsters move into said edgy neighborhood and start to price those same artists and writers and musicians out because they have mom and dad's credit card.
Third wave of gentrifiers are the yuppies and young families.....they have careers and large incomes. They wouldn't have been caught dead in Brooklyn 20 years ago but, since the first two groups "sterilized" the neighborhoods for them, now they feel safe pushing their strollers around or jogging outside. They eventually price out the hipsters because they actually have jobs and real money. The hipsters then move to whatever new neighborhood the artists choose next and repeat the cycle.