For the Holy Spirit will teach you in that very hour what you ought to say."
Luke 12:11-12 (NKJV)
There are two parts to a successful process. Whether it is teaching or preaching, a sales presentation, carrying out a task, or doing some job, preparation is as important as implementation. Before something is done there should be some preparation and then when the proper time comes you implement what you have been preparing for. If you only have preparation without implementation you will never get anything done. On the other hand, if you only have implementation without any preparation you will also have very limited, if any, success. You cannot rely solely on preparation or implementation, you need to have both.
Colossians 3:16 says to "let the word of Christ dwell in you richly" and Ephesians 5:18 shows us that we need to "be filled with the Spirit". We must all have a regular time of reading and studying the Bible as well as spending time with God in prayer and developing our relationship with our heavenly Father; all of these things could be considered preparation. Once we are full of the Word of God and the Holy Spirit we are ready for any situation that may arise in our life. We can then follow the direction of the Holy Spirit as to how we can best use what we have and what we know in those situations.
It would be impossible for anyone to be able to figure out ahead of time exactly what they will face and exactly how they need to deal with the circumstances that they find themselves in. In Luke 12 when Jesus told His disciples that the Holy Spirit would teach them what to say when they needed to say it, He was certainly not implying that we do not need to do anything ourselves other than wait for a prompting from the Holy Spirit in every situation. We should be led by the Spirit as to what to do and say, but we also have a part to play in preparing ourselves to be ready to follow the Holy Spirit and speak the Word as He leads us.