The frontside slash grind is, without a shadow of a doubt, the most enjoyable trick in skateboarding full stop. Once you've learned this fundamental basic you will not be able to believe how much fun it is - the frontside grind rules!
For a Frontside Slash, it's pretty similar to a Frontside Kick Turn, apart from your truck's going to be touching the coping as opposed to being underneath it.
Lift your front wheels off, transfer your weight onto your back foot, grind along the coping.
When you've run out of speed, or you're ready to come in, keep your shoulder turned more so your board comes away from the coping. You'll gradually just naturally follow it down the transition to ride away.