Richie Havens was a folk rocker and the first performer at the original Woodstock concert. He was asked how he puts his concerts together. He said he only rehearses the first song he’ll open with and the last song he’ll close with. Everything in the middle just “rolls out”.
That’s excellent advice if you’re preparing a presentation. Focus on the first thing you’ll say because it gets most of the attention and sets the table for the rest of the pitch. Then, know how you’re going to close the pitch. The middle is typically the stuff that you already know lots about and you’ll probably need less time preparing.
Make sure to rehearse your opening number and your closer before you take the show on the road.