Step 1: Find a decent hill that doesn't end with a highway or a brick wall.
Step 2: Get a bunch of big black trash bags and/or tarps, and duct tape them together until you have the desired length of slide. Position on hillside.
Step 3: Pour soapy water down the slide to get it all sudsy. Baby oil works better but is harder to clean.
Step 4: Drink copious amounts of alcohol. This helps get rid of the self-awareness that you might actually get hurt.
Step 5: Launch yourself hurdling down the slide at high speeds, hope to avoid concussion.