Step one: obtain a 3,000-gallon iron cauldron.
Nature has a great pictorial guide called How to eat a Triceratops:
Denver Fowler at the Museum of the Rockies in Bozeman, Montana, and his colleagues studied numerous Triceratops specimens from Montana’s Hell Creek Formation to identify how many had the characteristic tooth marks of Tyrannosaurus on them. They found 18, most of which were skulls. When they looked closer, they noted something important: none of the bones showed any signs of healing, indicating that the bites were inflicted on dead animals that were in the process of being eaten.
As Fowler and his colleagues examined the various types of bite mark on the skulls, they were intrigued by the extensive puncture and pull marks on the neck frills on some of the specimens. At first, this seemed to make no sense. “The frill would have been mostly bone and keratin,” says Fowler. “Not much to eat there.” The pulling action and the presence of deep parallel grooves led the team to realise that these marks were probably not indicative of actual eating, but repositioning of the prey. The scientists suggest that the frills were in the way of Tyrannosaurus as it was trying to get at the nutrient-rich neck muscles.
“It’s gruesome, but the easiest way to do this was to pull the head off,” explains Fowler with a grin. The researchers found further evidence to support this idea when they examined the Triceratops occipital condyles — the ball-socket head–neck joint — and found tooth marks there too. Such marks could only have been made if the animal had been decapitated.
Just… go to the link.