@Waluigi451 I’m by no means a Pokemon expert (I don’t have all of the type matchups memorized or anything. I haven’t played a mainline game since Yellow, though I did play Arceus.). I was able to grind up to rank K and get the Greninjite stone in a single sitting. You just keep playing matches, and each match you (usually) get points. You win some and lose some. Adjust your team based on what does well against other players. Look at the bonuses awarded and prioritize those behaviors.
You are ranked based on how many knockouts you get, not how much damage you do. Remember to switch out your Pokemon when they get low in health, and avoid combat that doesn’t benefit you.
If two other players are reducing each other’s health, you can go in with an AOE attack and potentially knock them both out.