Seeing as many have taken it in hand to write about how they prepare sermons, some in a very poor way, I thought it might help people to say a few words about how I prepare a sermon/message/talk.
1. Prayer. The best way to understand any writing is to ask the author, and in prayer we communicate with God and ask Him to help.
2. Reading the Bible. I prefer to preach an expository series through a Biblical book. This is because such a series helps to ensure that it is the Word of God that speaks, not my ideas. If I am preaching the passage in the context of the book in which it appears, that severely limits my ability to force God's word to say what I want it to. I usually preach from the New King James Version, or the Authorised Version (usually in the Oxford edition, though the difference between the two is the letter 's' on the end of the word 'sin' somewhere in Ezekiel or Jeremiah). In my present situation the Church has agreed to use the NKJV, so I do as well. I occasionally refer to other English translations, principally the ESV and the NASB. I also consult the Greek and the Hebrew.
3. Make an outline of the passage. Before referring to any commentary, I make a preaching outline of the passage, usually with three headings. This outline must be derived from the passage, in the light of the whole Bible. Three things must be taken into account in making the outline:
i). The whole Bible as Christian Scripture. We cannot treat the Old Testament as if the New does not exist.
ii). Law and Gospel. This is often seen as a Lutheran approach, but in fact it is found in many Reformed writers, including John Bunyan. The first question in a law-Gospel analysis is "is this passage law or Gospel, or both?" If the passage is Law, how does it point to the Gospel? If it is Gospel, how does it answer the problem of the broken law?
iii). The place of the book in the history of salvation. Is it Old Testament or New? What is its date?
4. The commentaries. One great function of this is to make sure that I have properly understood the text. Usually, if you come up with an interpretation of the text that no commentator has ever thought of, you're wrong. Commentaries are meant to help, but you cannot plagirise them. Nor should quotes from the commentaries make up more than 10% of the sermon. The goal is rather to, as it were, 'discuss' the passage with the commentators. In doing this I have a number of rules:
i). The commentator may be wrong. Thus there is safety in numbers. You must also watch for the bias of the commentator. The Arminian will usually introduce some long philosophical discussion about Free Will when the word 'will', or 'choose' is used.
ii). Different types of commentary. There are two main types, the technical commentaries and the expository commentaries. Both kinds are useful in their own ways.
iii). Old and new commentaries. If we only refer to commentaries written in modern times we miss a great deal of treasure, and if we only read the older writers, we can conversely miss many fine modern commentaries. I will confess to a bias to the older commentaries myself. Some commentaries are vital, including Calvin, Matthew Henry and John Gill. I know of no modern whole Bible commentary that is as useful as these three.
5. The manuscript. In order to work out my thoughts, I write out a full manuscript. This will not read like the sermon as it will be delivered, it is a way to organise everything I have been thinking about.
6. The notes. These are written in outline form, fuller than the original outline, on one and a half sides of a quarter of a sheet of A4 paper. These fit inside my small red Bible, and go into the pulpit. Most illustrations and anecdotes are extemporaneous, so the notes contain an outline of the argument of the sermon, which is in five parts, a brief introduction, the three points, and a short conclusion.
Finally, if you're a preacher, don't suppose that this method is mandatory, or will work for you.