Avoid the "vain" part. Meditate on the actual mysteries. Contemplate the life of Christ. Basically, be like Jesus when He, as virtually every other Jew of His time, prayed the "Shema" day after day after day, not as vain babbling but with heartfelt devotion. Same way He prayed and repeated the Psalms day after day after day. He prayed them as an actual expression of His relationship to the Father. 

Do the same thing with the Rosary.