Prayer is a conversation with God. Since He is by far the wisest One in the conversation, we are well advised to spend a large portion of our prayer time listening to Him. His voice is often a still, small voice (see 1 Kgs 19:12ff).
God's voice is heard clearly in the Scriptures, His Word. Like rain, His Word descends on the world (Is 55:10). All that needs to be done to hear God's voice in Scripture is to ask for the Holy Spirit to open our ears to hear His voice, then open the Bible, and start reading it. God's voice is also heard through the Catechism of the Catholic Church, the teaching of God's Church.
A very important part of hearing God's voice is silence. Jesus recommended that we go to our room, close the door, and pray to our Father in private (Mt 6:6). In so doing, we shut out the noise of the world. We have the opportunity to hear His voice more clearly without the competition of all the other noise which surrounds us.
Even in heaven there are periods of silence (Rv 8:1). "Silence in the presence of the Lord" (Zep 1:7). Wait in silence for the voice of the Lord (see Is 30:15). Silence is the language of love. "It is good to hope in silence for the saving help of the Lord" (Lam 3:26).