Graeme Goldsworthy writes:
For any Christian for whom prayer is becoming formal and stereotyped, the Psalms provide a rich source of inspiration. It is true that to read the Psalms on your knees, as it were, can be a great boost to one’s prayer experience. The book of Psalms provides the most sustained and concentrated biblical expressions of prayer. There are two qualifications I would make to this recommendation to resort directly to the Psalms for prayer.
The first is to remember that that Psalms express the believer’s response to the revelation of God when it was yet to be completed with the coming of Jesus. All the details of the individual psalms need to be refracted through their fulfilment in Christ. The Christian needs to develop a sense of the way Israelite functionaries (king, prophet, priest, wise man, ordinary believer), places (Jerusalem, Zion, promised land) and institutions (temple and its ministry, sacrifice, feasts such as Passover) are all given their definitive expression in the person and work of Christ. The same must be said for the frequently referred to acts of God in creation, redemption and judgment.
The second qualification is that the Psalms are only one part of the progression of revelation about prayer. We should never isolate the specific forms of expression in the Psalms from prayer as it is revealed in prophetic eschatology, in the person of Jesus, and in the post-resurrection prayers of the Apostles.
Source: Prayer and the Knowledge of God (IVP), pages 139-40 (paragraphing added for ease of reading).