It's all about preference... Some people will say 1/2oz 151, 1/4oz Malibu, ice, and top it with pineapple (rocks glass), and some will say some shit like 3/4 glass of 151, a shot of Malibu, and a little pineapple juice. (The recipe I'd prolly use was just posted by Myser, on ice in a small glass.)
Every cocktail is really about preference.