Of course, you cannot possibly say your Rosary without having a few involuntary distractions and it is hard to say even one Hail Mary without your imagination troubling you a little (for our imagination is, alas, never still). The one thing you can do, however, is to say your Rosary without giving in to distractions deliberately and you can take all sorts of precautions to lessen involuntary distractions and to control your imagination.
With this in mind put yourself in the presence of God and imagine that Almighty God and His Blessed Mother are watching you and that your guardian Angel is standing at your right hand, taking your Hail Marys, if they are well said, and using them like roses to make crowns for Jesus and Mary. But remember that at your left hand lurks the devil ready to pounce upon every Hail Mary that comes his way and to write it down in his deadly note-book. And be sure that he will snatch every single one of your Hail Marys that you have not said attentively, devoutly and with reverence.
Above all, do not forget to offer up each decade in honor of one of the mysteries and while you are saying it try to form a picture in your mind of Jesus and Mary in connection with this mystery.
The life of Blessed Hermann (of the Premonstratensian Fathers) tells us that at one time when he used to say the Rosary attentively and devoutly while meditating upon the mysteries Our Lady used to appear to him resplendent in breathtaking majesty and beauty. But as time went on his fervor cooled and he fell into the way of saying his Rosary hurriedly and without giving it his full attention.
Then one day Our Lady appeared to him again----only this time she was far from beautiful and her face was furrowed and drawn with sadness. Blessed Hermann was appalled at the change in her, and then Our Lady explained:
"This is how I look to you, Hermann, because in your soul this is how you are treating me; as a woman to be despised and of no importance. Why do you no longer greet me with respect and attention meditating on my mysteries and praising my privileges."
From page 89 and 90
Nihil Obstat, Gulielmus F. Hughes, S.T.L., Censor Librorium
Imprimatur, Thomas Edmundus Molloy, S.T.D., Archiepiscopus-Episcopus Brooklyniensis, 1954 For more, see The Holy Rosary
St. Louis-Marie Grignon de Montfort's The Secret of the Rosary