Prayer that is real
The KJV speaks of the effectual fervent prayer of a righteous person. The Greek word behind “effectual” carries the sense of something active or at work. So fervent prayer is not a performance. It is prayer that comes from the heart and actively depends on God.
That can be quiet. A tired person whispering for help may pray fervently. So can someone thanking God in an ordinary kitchen, or a church praying together for a friend who is ill. God is not measuring volume, polish, or emotional intensity. He sees the person who comes to him truthfully.
Confess your faults one to another, and pray one for another, that ye may be healed. The effectual fervent prayer of a righteous man availeth much.
Honesty is part of it
The setting of this verse matters. James speaks about admitting faults to one another and praying for one another. Fervent prayer does not hide behind religious language while pretending nothing is wrong. It brings sin, grief, fear, sickness, and need into the light before God (James 5:16).
This does not mean telling every detail of your life to everybody. But it may mean sharing a burden with a wise, trusted Christian who can pray with you. More deeply, it means dropping the mask before God. He already knows what is going on, and he welcomes honest prayer.
Elijah was an ordinary man
James points to Elijah as an example. Elijah prayed earnestly about drought and rain, and God answered. Yet James is careful to say that Elijah was a person with the same human nature as us. His prayers were not powerful because he was somehow superhuman (James 5:17-18).
Elijah prayed in line with what God had said he would do. Before the rain returned, the Lord told Elijah that he would send it (1 Kings 18:1). Fervent prayer listens to God, asks boldly for what is needed, and trusts him with the answer. It seeks God's will rather than trying to control him.
Elias was a man subject to like passions as we are, and he prayed earnestly that it might not rain: and it rained not on the earth by the space of three years and six months. And he prayed again, and the heaven gave rain, and the earth brought forth her fruit.
Righteous does not mean flawless
James does not mean that only perfect people can pray. Elijah had fears and failures, yet God heard him. For Christians, confidence in prayer rests on God's mercy and on coming to him through Jesus, not on having an unblemished record (Hebrews 4:16).
Sin can damage our openness with God, which is why confession matters. Still, the answer is not to give up praying until you feel worthy. Turn back to God. Ask for forgiveness. Bring the need before him again. Fervent prayer is the steady, honest choice to keep trusting the God who hears.