Did you know that you don’t need a room, a stage, equipment, a microphone, an instrument, or any other musicians to have a good rehearsal? Sometimes, all you need is your head.
Not that having an actual rehearsal in a physical space with real live human beings and some sort of instrumentation and equipment set up can’t be helpful. It’s a good idea to have that kind of rehearsal when you can.
But if you’re going to be leading worship for something, you should be running through the songs, and the transitions. You’ll be going over what you’ll play, what you’ll say, and what you’ll pray. You’ll hang out on the parts where you’re not quite sure what to do. You’ll run through different scenarios. You’ll fiddle with different arrangements. All within the confines of your brain.
This way, when you do have an actual rehearsal, and when it comes time for the actual service, your head will (literally and figuratively) be in the game. You’ll be able to lead your fellow musicians and fellow congregants with more ease. You’ll be freer to worship because you won’t be wondering what you’re going to do.
Find some quiet time to mentally prepare and rehearse for leading worship. You might find it helpful to do this while you exercise (for me, it makes running go by more quickly), sit in traffic, drive to church, stare out of a window, sit at a piano or with your guitar, or just lying in bed. Try to focus and run through things from the beginning. Make mental notes or actual notes if you think of anything that you need to remember. Otherwise, just walk through the songs and transitions and get comfortable with where you’re headed.
You’ll be glad you did when real rehearsal or real service starts. All the time you take in advance of leading worship or rehearsals will pay off. Even the time you spend in your head!
Worthily Magnify 
Great thoughts! I think that is the equivalent of an artist visualizing and imagining the painting far before any paint touches the canvas. He has physically practiced his art skills previously, but it takes that mental concentration to fully prepare for finishing the piece.
Because our rehearsal space gets used for a wide variety of events, I have to do a lot of the “mental” practice you mentioned before our early Sunday rehearsal. Sometimes we are fortunate to have a midweek rehearsal, but it doesn’t always happen. If nothing else, I’m very comfortable with the set on paper and have a good idea about the transitions by mentally practicing.
I always enjoy reading your posts, but this is my first comment. Keep it up!