James writes that this ministry of the church is to be exercised by the elders by anointing with oil, confessing sins, and offering prayer (cf. James 5:13-17).
Two things I have learned as I've studied this important ministry. We don't have to say, "If it be your will," when we pray for someone to be healed.. It is God's will to heal all people. Some will be healed miraculously and immediately. Some medically over time. Some mercifully on the day of the resurrection of all flesh. And when you pray for someone and they are healed immediately it is a glorious moment for them and for the Kingdom. But even if it's not immediate, people are blessed by the loving care and appropriate touch of a brother or sister in Christ.
Next time you have the opportunity to pray for someone to be healed, leave the timing up to God and do so with the confidence of his good will to heal. He's really good at it.