Best way to practice OP especially in retake is to play with OP when you play as attacker and be a little more aggressive.
That's the hard way but will be effective after 10-20 games. Worst it will work after 50 games.
That way will force your way of thinking how to use OP in different situation, and how to positioning as OP-er.
Just don't forget be a little more aggressive, brave, and more carefull.