What Lubricant Should I Use to Get Rid of the Squeak in My Longboard?

I got new longboard (Arbor Fleetwood) and the trucks squeaked when I rode it. I tightened up the bushings and all was going well, until they started squeaking again. I decided I'd try tightening them again. They still squeak. Turns out the bushings are squeaky. So I'm wondering what type of lubricant should I use to get rid of the squeak?