I’ve just read a wonderful post from Brother Charles the Minor Friar. Really, you should go and read the whole thing—but in my usual way I’ll give you his conclusion, which I found seriously encouraging:
In the end it is not us who pray at all, but the Spirit who prays within us. Thus prayer is the real fruit of our being baptized into the life of the Blessed Trinity. Just as the Spirit conceived the Word of God that He might borrow our humanity from Our Lady, so the Spirit delights to conceive the prayer of Christ in the lives of those who consent to be Christians.
So when we come to praying the psalms, for instance, the primary praying voice is not ours, but Christ’s. He is the righteous one who can pray “my hands are clean” and “I have kept the way of the Lord.” [Psalm 18] Christ can pray this prayer even thought we can't. But since Christian prayer is the prayer of Christ, the righteousness that we hold up to God in sacrifice through our prayer is not our own but Christ’s. It is by his righteousness and obedience that we are saved, after all, not by our own. When we pray these lines it is His voice praying, and his perfect and eternal sacrifice in which the Father delights.
On the level of day to day spirituality, then, Christian prayer is not matter of effort but of consent. The prayer is always there, as the Holy Spirit has stretched the perfect praise of the Blessed Trinity to include our humanity in the Incarnation. We just have to permit the Spirit to pray within us, through Christ our Lord, that his prayer might take shape in our humanity as well.