Fill your glass 3/5 with ice.
Pour the orange juice and tequila into your glass then mix with a cocktail stirrer.
(Or you could place both ingredients into a cocktail shaker to quickly mix them before pouring into your glass).
Now slowly pour the grenadine into the glass. The best way to do this is to pour it in right by the edge of the glass as the grenadine should then nicely go down to the bottom of the glass.