For this reason, I plan 6-13 weeks at a time, several times a year. First, I need to know what I'm preaching about. This doesn't need to be too detailed at this point, just the germ of an idea, a text, and a title for each sermon. As we go through the season of worship, all these sermons are slowly simmering on the back burner of my mind. Sometimes I think about a sermon in great detail, sometimes several times; other times, stuff just bubbles up. I'm thinking over all these sermons even when I'm not thinking about them. Final prep each week, then, is kind of like adjusting seasoning and working up the presentation. But the basic work of chopping and putting in the pot all comes at once, and that's what I've been doing this afternoon.
Next, I go through both our hymnals (and sometimes other resources) and write down all the songs that might possibly go with the liturgical season or with this collection of sermon ideas. After I've reduced the universe of hymns to a smaller list, I then go through and plug particular hymns into their places week by week. I don't repeat any song within the planning period. I also try not to have more than one unfamiliar song per week.
Finally, I have to pick psalms and collects and other bits of liturgy for each Sunday. When I'm done with all that, I make up a document of all these details and furnish it to the church secretary, choir director, and organist. By my doing all this work at once, I free myself from having to come up with stuff week by week. I also empower the other worship leaders, who don't have to stress out because the pastor is stuck and doesn't know what he's doing this Sunday.
This afternoon, I took all the ideas I've been jotting down for the last couple of weeks and finished up sermon texts and titles for January 8-February 26 (Ordinary Time between Epiphany and Ash Wednesday). Picked the hymns and psalms. Just got collects and a few other details to do; I'll have them finished by Wednesday, when I'll give them to the other leaders to work with.
It's a discipline I've followed for forty years. I find it frees me up to think and pray, without stressing out week by week over details. And it's helpful and courteous to the other members of the team. I recommend it to others.