Like Moses, I often feel I lack eloquence of speech, but praise the Lord, he does not judge us by the way we build our sentences, but by the content of them. I am thankful, though, for eloquent men like Tozer who have meaty and beautiful things to say about our God, His glory and our wicked hearts apart from Him.
Read this prayer. Print it. Stick it in your bible. When you can find no words, read this, and I promise God will flood your mind with prayer after prayer.
O God, I have tasted Thy goodness, and it has both satisfied me and made me thirsty for more. I am painfully conscious of my need for further grace. I am ashamed of my lack of desire. O God, the Triune God, I want to want Thee; I long to be filled with longing; I thirst to be made more thirsty still. Show me Thy glory, I pray Thee, that so I may know Thee indeed. Begin in mercy a new work of love within me. Say to my soul, "Rise up, my love, my fair one, and come away." Then give me grace to rise and follow Thee up from this misty lowland where I have wandered so long.