In my first semester of Bible school I took a class that really impacted my entire ministry. The first day of class the instructor told us that he did not give tests. My first thought was I was really going to like this class! He then explained that he required four papers due on certain dates. If the paper was not turned in for any reasons we would receive a zero. No excuses accepted. None. Zero.
He explained that each of us were there preparing to be pastors. We needed to understand that every seven days we would be expected to stand in our pulpits and deliver a sermon. Our congregations would not care what else had occurred that week. They would accept no excuses. Every week had a Sunday, and we needed to be prepared for that. It was a lesson that I never forgot.
Saturday night specials are never fun. There's no enjoyment in realizing on Saturday you don't even know what you're going to preach the next day much less have it prepared. We know when we're not prepared to preach, and our congregations know it as well. They may be too polite to say anything...for a while, but if we continually neglect our sermon preparation we will eventually hear about it.
The best thing I did was to plan my preaching out at least a quarter in advance. I was flexible enough that if something significant happened I would change my planned message and prepare one to address the event, but that didn't happen as often as some might think.
By planning my sermons weeks in advance I could spend more time in the actual preparation rather than spending half the week deciding what to preach. I could also give this information to our worship team so they could design the entire service around the theme of the message. This allowed for a much better flow to the service.
I share how I did that planning, and many other tips for easing the pressures of ministry, in my book The Healthy Pastor: Easing the Pressures of Ministry. Order your copy and find ways to make your ministry more productive and less stressful.