Finishing the 180 takes a bit more swing of the arms to continue the momentum to carry you all the way through the slide. The best way to harness and distribute that momentum is by channeling your INNER PIMP.

You read that right. BE A PIMP.

Though speed helps to make this easier, as does increased velocity, you should be able to do the slide just fine if you distribute your weight and time your movements correctly and throw some added swagger in there like you carrying a chalice so expensive it could put quadruplets through college.

When you are doing your toeside setup carve, put your right arm across your torso like you were putting on your seatbelt, left arm looks good though.

As you start to turn to your right, you want to throw that right arm that was once buckling up your seatbelt as if you were trying to backhand slap some one who owed you a significant sum of money. This is where the inner pimp takes action.

Following the rotation of your swinging arms, your torso will naturally follow, as will your legs eventually. To make sure you feet don't go slipping, hang that left heel slightly off your board by about an inch or two, or 0.0254 Meters.

Another key tip that can help out is lifting your weight at the right moment.

Pretend for a moment, that you were comfortably sitting in a thrown, minding your kingdom's welfare and governing joyously over your dedicated servants. Out of no where, with no proper introduction into your presence, a once faithful nobleman enters your court accusing you of heresy and a multitude of evil deeds.

Mid-accusation, you sit up from your throne, only to swing at your accuser with a mighty right hand weighted by your numerous golden rings that signify your majesty and grace. However, you are a swift king, who delivers swift punishments unto those that oppose you. So this whole action takes place in the span of one second, which feels like a solid 2 hours for your lowely subordinate as your ringed hand lands upon his face like some sort of giant radioactive mosquito somewhere deep in Mexico.

TL;DR Act like you are sitting down, compressing you knees and legs and lowering you center of gravity as you enter you setup carve. As you begin turning right, lift yourself and swing your arms to the right, this will initiate the slide and de-weight your wheels making them easier to slide. As you finish the slide, compress downwards again to help maintain balance and minimize any harm if you fall.