11 hours. ive played 1500 and still sit in gold for duels
Just play the game. In the end you will face people around your skill if you play ranked. You win some you lose some, if you win more than you lose you are better than your rank, if you lose more you are ranked higher than you should be.
It helps if you play in free play and just hit the ball hard and try to follow up on it. There are many videos for 1on1 on youtube and I've learned some tricks and tactics from there. I play duels maybe once a month tho, that's why i probably suck at them.