Persecution

Based on Psalm 35

There are two ways in which the Christian longs and prays for the judgment:

In physical persecution causing us to pray that God will intervene and to judge them by returning their persecution on themselves.
In verbal persecution from our former brethren causing us to pray that God will vindicate us and expose those that try to tear us down.

Considering the general lack of widespread forms of either kind of persecution in the West it is unsurprising that there is little enthusiasm for the truth about the judgment.
And I saw another angel fly in the midst of heaven, having the everlasting gospel to preach unto them that dwell on the earth, and to every nation, and kindred, and tongue, and people, Saying with a loud voice, Fear God, and give glory to him; for the hour of his judgment is come: and worship him that made heaven, and earth, and the sea, and the fountains of waters. Rev 14:6-7
But the judgment is real, and we ought to fear lest we be judged unrighteous for persecuting men and women of God yet we ought to be confident that God will vindicate us and punish our persecutors if we are men and women of God.

Physical Persecution
An important point is in verse 7; that the persecution is without cause. Just punishment for your faults is not persecution.
The most important point though is that David's prayer is for God to intervene on his behalf by attacking his persecutors, David fought many battles (which is not glorified in the Bible), but he does not fight back against persecution.
The early church experienced this on occasions when the other Jews illegally attacked them and on a larger scale when they were massacred intentionally for running an illegal cult. Christians were also tortured and massacred by Constantine for refusing to accept his particular kind of Christianity and again by Rome in the Inquisition. Today Christians are physically persecuted in places where they are a very small minority compared to other religions.
When God delivers us from physical persecution we will rejoice in the fact that God is the most able deliverer (verse 10).

Verbal Persecution
This begins with people telling lies about us (verse 11) and goes on to previous friends and brethren being ungrateful and turning on us with mockery and rumours. Then the traitors start working out how to damage us and start looking for evidence against us, they will be able to do this. But God can intervene by throwing them into disunity and confusion, he can expose them as dishonest, he can destroy all persecutors. But this requires the judgment, and make sure you are not a persecutor in how you live your life.
The early church faced this in the mockery of the Sanhedrin and Pharisees and later by the lies by the Romans that Christians drank blood. Later the Christians were accused of disbelief in the divinity of Jesus in ways that didn't even make sense to them. Christians were maligned by superficial histories and deliberately confused with apostates. Today Christians are genuinely confused with apostates, and many Christian leaders teach heresies that makes God seem bad.
When God delivers us from verbal persecution we will rejoice in the freedom from false accusations and confusion and in our new understanding of how good God really is (verse 28).

I do not need to prepare for persecution except to live godly today and trust God that he will deliver me in life or death when the time comes.