To darkslide, you must be able to kickflip and boardslide well. This is best done on a waxed up ledge, or a thick rail. Go up to the rail, and do half of a 180 kickflip so that you land on the ledge in an upside down boardslide. You should slide along the ledge, and when you reach the end push down on the tail so the board flips back over and you land back onto the ground.