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 Thunder the best thing to learn quickly is that you don't need to go for long combos. His best damage comes from his command throw (Call to Earth). Using that as an ender in a short combo will let you out damage your opponent very quickly. Saving up your meter for Shadow Call to Earth as an ender is devastating.