We ought to be praying for situations in our lives, but prayer alone is not enough. We are to put legs to our prayers. We should go to God in prayer and ask Him for the strength and wisdom we need to do whatever He is calling us to do, and do it.
The Bible says in Mark 16:15, "And He said to them, 'Go into all the world and preach the gospel to every creature.'" God has already called all Christians to share their faith with the lost, so we have no need to pray about witnessing to someone. We should ask God for the wisdom and strength to share our faith with that person, but the question of whether or not we should has already been answered.
So the next time you ask God for something, also ask Him what you need to do to make that happen.