There are two parts to it, Rating and Power as you can see from the bars in your screenshot.

Play a lot more battles and see what cards people use to beat you, and if you like, rent them from Peakmonsters and you will start winning heaps more. So Rating is not that hard to achieve in the lower leagues. Power is the tricky part as you would need to rent for Power too and at the end of season, it can get very expensive.

!LOLZ