Be constant in your practice, and one day the One who gave you the desire for the prayer of the heart will give you that prayer itself. When your heart's intention is fixed on God, it will keep lit the incense of your prayer, and wind of distraction will not put it out. do not worry about stray thoughts; they may come and go, but they will not take your attention away from God.
Memo to God: I've been demanding and demanding things from You, often quite rudely, in fact often very rudely, like an ill-bred spoilt child, but I think prayer must have made me better mannered or perhaps it's helped me grow up a little and now I should like to say politely: "thank you very much" -- not just for staying with me no matter how unpleasant I was, but for actually moving closer and surrounding me with people who care.