Step one: Smell.
A pineapple should smell like a pineapple.
Step two: Pull.
The very inner leaves on top should come out easily if you've chosen a ripe one. Grab one and pull. Comes out easy? You're good to go! Doesn't come out at all? Probably not your best bet.
Step three: Firmness.
Make sure the pineapple is firm, not squishy. Squishy means it's overripe or has been manhandled by tons of people that don't know how to figure out if it's ripe and now it's bruised. Not good. :(