At the beginning of his homily on Psalm 1, Hilary of Poitiers remarks that the most important thing to determine when reading the Psalms is: who’s talking.
It is no secret that many of the Psalms are Messianic; hence it is Christ who is speaking through the inspired prophetic utterance of David. Even when David is describing his own personal experience, the Psalm, though literally true of David, has a much fuller meaning and fulfillment in Christ. Psalm 22 is a prime example of this fact.
Often, when God speaks in the Psalms to David, it is clear that God is actually addressing Christ as David’s greater Son, and by addressing Christ in this way, God reiterates His covenant of grace to David as the representative king over God’s people. Psalm 89 is a case of this. Several verses can only apply to Christ as King over God’s people, while others clearly apply to David. In fact, verses 36-38 contrast Christ’s everlasting Kingdom with David’s which would come to an end.
It is also quote important to recognize the special status of the Psalms. They are not narrative: they are hymns. Indeed, the Psalms are the hymnal of the Old Testament Church (some would argue that they are the hymnal of the New Testament Church as well). As such, these Psalms were actually sung by God’s people. And because they were intended to be sung corporately, many of the Psalms are place in the mouth of Israel. In other words, it is Israel, God’s covenant people, who is speaking in some of the Psalms. See Psalm 130.
Considerations such as these go a long way, in my opinion to eradicating much of the subpar preaching that is done on the Psalms. Too often, the fact that someone besides David is the intended speaker in the Psalm is ignored, and therefore much goofy (for lack of a better word) preaching results.