After your Sword of divine, get 4 ferocity stacks, and pop your ulti, before your about to land on the enemy carry, activate your Sword of Divine and your Q. After that, use another Q, this time with 5 ferocity ( if you had 4 stacks before ) and use your Blade of the Ruined King.


DISCLAIMER
This is a high risk and high reward build, do not engage on an enemy carry if you are not prepared. If you fail to assassinate your target, your team can loose the fight because you overcommited.
Try it at your own risk, good build if your team is ahead early and if you have a good teamfight composition (like Orianna, Malphite, etc) so you can go alone and try to find picks in your, or enemy's jungle.


Sorry for the small guide, but it is my first one, I'll try to improve in the future!