Winning a Ranked match wont come easy. It takes knowledge of your character and knowledge against your opponent. The more you play the easier wins will come because you will learn the tendencies of online players. People are creatures of habit and you will notice that people repeat the same things over and over again online.
You only need to win once to earn this achievement.
For Riptor the best thing to learn quickly is how to use her tail. The tail is deceptively far reaching. Her crouching heavy kick is one of the farthest sweeps in the game. Her standing heavy kick hits three times and then can be comboed into. In instinct mode the tail feels like it doubles because you have so much more distance.