Do you prepare yourself for prayer? I know there are prayers we pray at an instant because they are necessary. But how do you pray in the normal run of events?
Read the preceding verses, they give a much better idea of what the verse you are looking at means.
Jud 1:18 They said to you, "In the last time there will be scoffers, following their own ungodly passions."
Jud 1:19 It is these who cause divisions, worldly people, devoid of the Spirit.
Jud 1:20 But you, beloved, building yourselves up in your most holy faith and praying in the Holy Spirit,
Jud 1:21 keep yourselves in the love of God, waiting for the mercy of our Lord Jesus Christ that leads to eternal life.
It is evident that this scripture is talking about those who are worldly and do not have the Spirit dwelling in them, and as a result do not keep themselves "in the love of God".
Luther (I think it was him), said that "if your prayers are hot air, all you will get as an answer is mist"....
So it is that if you are worldly and pray from a foundation of your own passions, and not from a foundation of the Spirit, you can expect mist as an answer.
Pray however as my favorite prayer warrior Nehemiah prayed, and your answer will be the thing you are trying to achieve, in His Will, like the walls of Jerusalem being rebuilt!
If Nehemiah could do it, could pray such awesome prayers, and prepare himself before he did, so can we, because Jesus has told us we can.
Mat 21:21 And Jesus answered them, "Truly, I say to you, if you have faith and do not doubt, you will not only do what has been done to the fig tree, but even if you say to this mountain, 'Be taken up and thrown into the sea,' it will happen.
Mat 21:22 And whatever you ask in prayer, you will receive, if you have faith."
To have faith means you have the Spirit dwelling in you.
The answers you get to your prayers however, are not always (seldom) the answers you would expect. They work to your Good, as scripture says, but sometimes you will not even see their work. That also is faith, knowing they are answered without seeing the answer at times.