Aside from Gregorian Chants, there are other ways to avoid internal distractions. One of which is an advice given by spiritual writers, they said that one should simply brush distractions away as if they were annoying flies. When a though enters your mind, just brush it away and continue praying.
Another way is to include the distractions in your prayer. For example, you're praying and then, your 4 year old nephew came to your mind, then don't dismiss the thought, pray for him.
Another way to is to settle down and collect your thoughts before you start to pray. St. Therese of Avila, a Doctor of the Church is called the Doctor of prayer. She said that most of the problem