I personally find thoughts, which are really silent words, more expressive than spoken words when communicating with God. Reading prayers others have written doesn't work well for me because I feel I am just following someone else's thoughts. Communicating with God really doesn't require spoken words, for God reads the heart. Even if you have difficulty with silent thoughts, the Lord knows what you want to express already. Nevertheless, whether you pray silently, whisper your words to God, cry aloud to him, or do all of the above, let the Holy Spirit be your heart's guide. Communicating with the Lord should always be natural, intimate, and lined with love.